How do you know that the world is round? That might sound like a stupid question, but there are a surprising number of people who doubt that the world really is a globe. There’s even a society. Here’s their logo! Since childhood, these people have been taught that the world is round. But for some reason they no longer feel convinced that what they have been told is true. I read about one woman who decided to take matters into her own hands and find out once and for all whether the earth was round or flat. She undertook a very scientific experiment. She went down to the sea, taking with her a long straight stick. Then she held up the stick against the horizon to see whether the horizon was flat or curved. It was flat. Conclusive scientific evidence that the world is flat, right?

We might laugh at this woman’s silly attempt to prove things for herself. But don’t we as Christians act a bit like that sometimes? Since we became a Christian - many of us since childhood - we’ve been told about Jesus. But sometimes we find ourselves doubting what we’ve been told. I don’t mean that we doubt the facts of Jesus’ existence, life, death, resurrection. It’s true that we might sometimes doubt those things. But I think most of us have a different kind of doubt. We know it all really happened, but we struggle to believe the full significance of what happened. In church we sing “Behold our God, seated on his throne” and “Our God reigns”. But next week when you find yourself almost unable to resist that same old temptation, next month when you find yourself put in a compromising situation at work, next year when you’re lying in a hospital bed, suddenly it seems very hard to believe that Jesus reigns. We take communion and remember that Jesus died to save us from our sins. But three days later, as you face the shame of yet another day of failure as a Christian, three months later, when your colleague says it’s intolerant to suggest that only Jesus can save and that all religions are basically about making this world a better place, thirty years later, when you lie on your death bed and wonder if you have done enough for God to accept you, suddenly it seems very hard to believe that Jesus saves. And I think no Bible story highlights this problem more than the Christmas story. Most of us are happy to sit through yet another nativity play and accept the reality of these familiar events. But what difference does the baby in the manger make on Monday morning? Do we firmly and passionately believe - in our heads, in our hearts, and in practice - that this baby is our Lord and Saviour?

Perhaps you long for deeper assurance of these things. But have you ever felt that all your efforts to find deeper assurance have been completely in vain? A bit like the woman whose best attempt to get assurance was to hold a stick up to the horizon. Wouldn’t it be great if this Christmas was different? If this Christmas Jesus could be real in your life like never before. If this Christmas all your doubts could be chased away. If this Christmas you could say with the deepest assurance that the baby in the manger is your King and Saviour. Fortunately, one of the Bible writers understood our problem: Luke. He understood our first point:

THE ASSURANCE WE NEED

Have you ever received a credit card in the post from some random company and you just threw it right away because you knew you couldn’t trust it? Well, let me tell you about a guy called Theo, who gets a bank card in the post one day from his friend Lucy. Except it’s not a credit card, but a debit card for a major bank. Lucy explains in a letter that she received two cards in the post and was sending one on to him. She claims that it will allow him to make withdrawals from a back account holding millions of francs. Normally Theo would trust Lucy, but this seems too good to be true. He eyes the debit card suspiciously. Could it be a scam? Or could it be real? Straight out to the nearest ATM? Or straight out to the trash? At that moment, the phone rings. It’s Lucy. “Do you need some reassurance?” she says gently.

Well, in the introduction to his Gospel, we find Luke writing to a friend to reassure him in a similar way…

Read Luke 1:1-4

Luke writes to a guy called Theophilus. This guy sounds a lot like us. He wasn’t one of the first eyewitnesses of Jesus’ life, death and resurrection. However, he’s been taught quite a lot about Jesus. He’s probably a Christian believer, or on the verge of becoming one. But did you see that he lacks “certainty concerning the things [he has] been taught”? I don’t think that his problem is that he doesn’t believe the events actually happened, since why would Luke think that simply rewriting the story is going to persuade him? After all, he has heard eyewitness accounts. I think that Theophilus, like most of us, believes that the events were real. But, like us, what he lacks is a deep assurance of what these events mean for him. Perhaps, like us, he’s wondering, “but how can I really know deep down that Jesus is Lord and Saviour? How can this become more real to me?” He’s holding that debit card in his hand, not sure what to do. His problem isn’t with believing that the card exists. His problem is knowing: is this the key to unlocking millions of francs, or is it another fraud? Is that what Christianity is for us? Just a debit card sitting unused in your pocket because you’re not sure it really works? That’s why Luke writes to give him deeper assurance that the debit card really works.

I find that hugely encouraging. That God doesn’t condemn us for needing more assurance. He provides a whole book of the Bible deigned to give us the assurance we need! But what is Luke going to say to give Theophilus deeper assurance?

THE PROMISE WE NEED

Let’s read the first thing Luke writes.

Read Luke 1:5-10

Are you thinking that what Luke chose to write is a little surprising? What does he do to reassure Theophilus? He tells him a story. A story that doesn’t appear in any of the other Gospels. A story that at first glance seems a bit odd. But this story is very carefully chosen.

It’s about a guy called Zechariah. This guy is a good guy. He’s a priest serving in God’s temple. His wife is also descended from Aaron the Great High Priest at the time of Moses. What’s more, they are both “righteous before God, walking blamelessly in all the commandments and statutes of the Lord.” Of course, we know they must be far from perfect, but this expression is often used in the Old Testament to mean that they take God’s law seriously and seek to serve God faithfully. So far so good. But all is not well for this couple.

Firstly, they have no children. Elizabeth is unable to conceive, and they are both old anyway. In those days, childlessness was like the ultimate shame. And secondly, in parallel to their personal tragedy, we are reminded of Israel’s tragic situation. Zechariah is given a once-in-a-lifetime opportunity to burn incense in the temple. Burning incense was a special ritual performed every day by a different priest. It accompanied a time of intense prayer, making requests to God. What do we imagine that Zechariah and the crowd outside were praying for? Well, a little bit later, Luke speaks of a man in the temple who was “waiting for the consolation of Israel.” And he also says that many “were waiting for the redemption of Jerusalem.” This was a time in Israel’s history where many were praying fervently for God’s Old Testament promises to come true, For him to send the promised Messiah to save them from their enemies. For him to end his 450 years of silence.

So why is Luke telling Theophilus about Zechariah? Well, because here is a guy massively in need of assurance. In fact, Zechariah has far less to go on than Theophilus. Zechariah has no children and no Messiah. But he’s about to become the first person in history to get full assurance of these things. And Luke wants Theophilus to read it. So Luke doesn’t hand Theophilus a phone so he can ring God to get some special assurance just for himself. Nor does he give him a test tube so he can put the facts in it and analyse them. He writes him a story, so he can look more closely at what God has already done to give assurance to mankind. And where better to start than the very first time God gave that full assurance?

So what is the assurance that God gave to Zechariah? Let’s read what happens next.

Read Luke 1:11-17

Put yourself in Zechariah’s position. You’re a tired old man. You’ve been waiting all your life for children, not to mention the liberation of your country. Now you find yourself on the most important day of your life, performing this special ritual. I wonder what was going through his mind as he lit the incense and lifted his eyes to heaven to offer yet another plea for his family and for his country. I bet he was not expecting an angel to appear. Certainly his response is not delight that an angel came in answer to his prayer, but terror! But Zechariah doesn’t need to be afraid. For the angel has been sent to bring assurance for this long-suffering old man. His prayer has been heard. And God is going to speak for the first time in 450 years! What’s the message? God is going to give him a son. And even better, that son will signal the beginning of God’s salvation of Israel.

To understand fully what God is promising here we need to see the number of allusions to the Old Testament in this passage. This is not the first time that a couple have been childless. Abraham and Sarah were too old to have children. Hannah the mother of Samuel was barren. On both of those occasions God caused the birth of a very special child. Abraham and Sarah had Isaac, the proof that God was going to fulfil his promise of salvation to Abraham’s descendants. And Hannah gave birth to Samuel, Israel’s first prophet, who prepared the way for King David. The birth of John looks a lot like God is about to do something in the same vein. Furthermore, the angel compares John to Elijah. This is partly because he will have the same role as Elijah, to call Israel to come back to God. But it’s more than that. Here’s what the prophet Malachi spoke, and look how similar it is to what the angel says about John.

Read Malachi 4:5-6

And a bit earlier in Malachi, God says:

Read Malachi 3:1

So John is the new Elijah that God promised would come just before the Messiah comes. John will have the incredible role of calling people to repent of disobeying God and come back to him, so that they will be ready to receive the Messiah, who will arrive very soon! So John’s birth means that God is on the brink of fulfilling everything that he had promised. The promised Messiah really is coming. Salvation really is possible.

That’s some pretty amazing assurance for Zechariah. Israel may look like they’re in a hopeless situation. But the angel reminds Zechariah that God had made countless promises in the past. And then Zechariah gets his own personal message from God to reaffirm that, not only does God still intend to keep these promises, but it is going to happen very soon! What more assurance does he need?!

To go back to our debit card story, how would Lucy reassure Theo that the card is genuine? Well, Lucy tells Theo about another friend of hers, Zach. Zach’s dad is a bank manager and has his own account containing millions. Ever since Zach was a child, his dad had promised him that he would one day give him access to the account. He had to wait a long time, but finally he received three debit cards from his dad, along with an official letter declaring that he had access to the account, as promised. This was enough to assure him. But he didn’t need three debit cards. So he sent two of them to Lucy. Lucy didn’t need both cards, so she sent one to Theo. “So you want assurance that it’s real?” Lucy says to Theo, “well, what if I get Zach to show you the official letter from the bank, will that be enough to convince you?” You see, Theo doesn’t need any special proof especially for him. The official letter, along with the promises originally given to Zach, is more than enough.

Now in our story, Theo is of course Theophilus, Lucy is Luke and Zach is Zechariah. Zechariah gets the reassurance first hand from God, like getting an official letter. The good news gets passed on to Luke, and later to Theophilus. But Luke and Theophilus don’t need to get their own “official letters” from God. The original words that God spoke to Zechariah - not to mention all his promises in the Old Testament - that’s more than enough. And the same is true for us. If we want deeper assurance, we don't need God to do anything out of the ordinary especially for us. We simply need to take another look at what God said here to Zechariah. Like Zechariah, we simply need to remember all the promises that God made in the past. Like Zechariah, we simply need to take this renewed promise from God seriously and rejoice with full assurance that the promises really are coming true. Jesus really is the promised Messiah. Salvation in Jesus really is possible.

But there’s a surprising twist to this tale in our final point.

THE REASSURANCE WE DON’T NEED

How would you expect Zechariah to react to the angel’s news? Let’s read the end of the story and find out.

Read Luke 1:18-25

At first glance, maybe you thought Zechariah’s question appeared to be a fair question. After all, when the angel announced the birth of Jesus to Mary, she asked a similar question: “how will this be, since I am a virgin?” But Mary wasn’t rebuked for her question and Zechariah was. There’s a crucial difference. Mary wasn’t questioning the truth of the angel’s message. She was simply wondering how it was going to happen, since she was not married! But Zechariah, as the angel points out, “did not believe”. It was just too impossible for him to believe that easily. Could the angel not offer him a further sign, perhaps? But he is immediately rebuked for not believing. After all, as the angel points out, this is a message directly from God. Not to mention all the promises laid out in the Old Testament that the angel has alluded to. Isn’t that enough to give Zechariah full assurance? So the angel does give Zechariah a further sign - he becomes mute, unable to speak. But it’s rather an ironic sign, don’t you think? It’s as if to say, “OK, here’s the sign. But because you didn’t trust God’s words, the sign will be that you will not be able to speak your own words until God’s words come true.”

The good news is that Zechariah did believe after that. In fact, after John’s birth, Zechariah’s speech is restored. And he declares his belief in all that God had promised to do through John and then through Jesus. Zechariah got his full assurance, in the end. But it must have been a painful lesson. It would have been a constant reminder that he should have believed God’s words straight away, even if he would have to wait for them to be fulfilled.

I think Luke wants to highlight something here. It’s not wrong to need reassuring. But there’s a point where we don’t need any more reassurance. It’s the point when we’ve heard and understood God’s promises. After that, Zechariah is wrong to ask for more reassurance. It’s the same for Theophilus, and also for us. “I know you need reassurance,” says Luke, “but don’t make Zechariah’s mistake of demanding more assurance than you need. If God has said it, that is enough.” And we might add that Theophilus and us have the advantage of having seen many of God’s promises come true already.

You may know of the mental health condition Obsessive Compulsive Disorder, or OCD. This condition is sometimes called the “Doubting Disease”. OCD sufferers effectively find it impossible to feel certain about things that most of us don’t even give a second thought to. Now I don’t want to make light of OCD, because it is a very serious condition. But in a sense I think all of us suffer to some extent from a “doubting disease”. Like Theophilus, it is right to want a deeper assurance. But when we have heard and understood God’s promises that he spoke to people like Zechariah, that should be enough to give us full assurance. But sadly, the doubting disease often persists even after this.

This passage got me scratching my head. In what way does the doubting disease affect me? In what way do I doubt, even after hearing and understanding what God has promised? A helpful exercise is to read Zechariah’s speech after John the Baptist is born, later in chapter 1. This tells us what Zechariah came to believe, based only on what God had spoken. Let’s see if you have trouble believing any of these things… That Jesus is the centre of God’s plan for the world and for your life? That God’s promises are intended directly for you? That God desires to show you tender mercy? That Jesus has paid for all your sins at the cross, no matter how big or how frequent? That God desires to give you light and peace in your walk with him? That you were called to serve him without fear? That Jesus is King of every part of your life? That God will fulfil what remains of his promises, even if you have to wait a long time? Zechariah understood all those things, just from what God had spoken. Yet I know I can doubt all of those things at one time or another, whether in my head, my heart, or even in my actions. Now, you may not struggle with doubts as much as I do, but I suspect that we all have the doubting disease to some extent.

When we doubt, let’s remember the lesson that Zechariah learned. What God has spoken is enough. That sounds obvious, but try it next time you doubt and you'll probably find it’s harder than you think. That’s because we feel like we need to take matters into our own hands. Perhaps we ask God to speak directly to us. Or we want some deep inner experience of reassurance. Or we want to reason it through with logical arguments. It’s hard to simply say, “God said it, so I believe it.” But that is what God is asking of us. God has spoken. God has promised. That is enough.

Remember the woman who tried to work out whether the world was round or flat. Well she tried to take things into her own hands and failed miserably. But the testimony of countless scientists and travellers ought to have been enough to convince her that the world is round. When someone trustworthy gives you their word, you don’t need to find your own proofs. This Christmas, let God’s Word give you all the assurance you need.