1) Because I am alive. I've never been able to get over the surprise of this. It seems completely unlooked-for and gratuitous. It fits with the idea of a God who didn't have to create anything, but did so out of pure love.
2) Because the world is so dramatic. Nothing had to exist at all. But, given that something does exist, why wasn't it a static, lifeless, unchanging mass of some kind? Or, on the other hand, why wasn't it a chaotic flux with no pattern, no form, no breathing space? As it is, we have a playground for the human intellect, a theatre for the human soul. (I am partly indebted to Carl Sagan for this point. He was merely pointing out how the universe we inhabit allows the emergence of science. He might have been horrified if he realised he was planting a seed of theistic belief in an innocent teenager's mind.)
3) Because things are fundamentally good. We hear a lot about the "problem of evil", but not about the "problem of good". Most of us can expect to live out this day, and the one after that, and the one after that. We can expect that the person sitting next to us on the bus would sooner help us than hurt us. Most of the things we do every single day bring us joy, from the first scoop of breakfast cereal to the caress of a soft pillow on a tired head. Even the things we don't want to do, like working or exercising or waiting in a queue, often end up bringing us an unexpected satisfaction. Whose fault is it that we become blasé about such abounding joy?
4) Because of my thoughts. I am unable to conceive how my memories of a Christmas morning twenty-five years ago are basically made of the same stuff as a pebble, a screwdriver or a tub of lard. I am not sophisticated enough to understand eliminative materialism, just as I would gape at someone who told me that, from the viewpoint of advanced mathematics, two and two actually equalled a pear tree. And the fact that my thoughts seem somehow outside the realm of the physical makes me unable to believe that only the physical realm exists. It also makes me think that there must be an intelligence behind the universe, on the grounds that the greater cannot come from the lesser.
5) Because I have an idea of good and bad. Though I am often successful-- spectacularly successful-- at rigging those notions of good and bad to line up with what I want to do, now and again I find they become stubborn and won't cooperate. Besides, why should I even want to rig them? Why not just ignore them? And I find that other people not only have these notions, but have them to a degree far in advance of myself. It seems as though my notions of right and wrong have a source outside the physical world, too.
6) Because of Jesus Christ. Talk about a magnetic personality! Even the enemies of Christianity seem unable to find anything to say against him. Bertrand Russell accused him of petulance for withering the fig tree that would yield no fruit. It wasn't one of Bertie's better moments; this is plainly a kind of concrete parable for the benefit of his disciples.
I don't know of any character, real or invented, who combines an air of absolute authority with utter humility, as does Christ. He is not some stoic, otherworldly, blissed-out sage, as one might expect of a visitor from the heavens. And yet, how banal that would be! But no; Christ weeps, becomes irritated, has a flair for the dramatic, and dreads his final suffering. And yet every word he spoke seems to glow with irresistible truth.
7) Because of the saints. The saints have the paradoxical quality of being fanatical and yet not fanatics. They were men and women addicted to doing good in the way a teenager is addicted to video games. But, though they seemed to have a kind of craving to feed the poor and comfort the afflicted, none of them seemed to find that these practical acts of charity clashed with spending long hours in prayer and devotion. It even seems as though the two things are-- contrary to appearances and the "social gospel" critics of the Church-- actually one thing!
When you have a group of witnesses who stick to their guns through every persecution, who are even willing to give up their lives for the truth of their claims, and whose stories "check out" with one another to an extraordinary degree, you begin to think there is something to what they are saying.
8) Because of the Catholic Church. Whatever else you may say about the Catholic Church (and everything else has been said, at one time or another), it is undoubtedly the greatest show on Earth. It has run and run and run-- through the rise and fall of empires, the birth of nations, the passing of whole civilizations. I don't know how to account for its survival through persecution, schism, wicked Popes, ideological opposition and the utter changing of the world. What keeps the show on the road? I believe it is the Holy Spirit.
9) Because of the banality of secularism. I cannot believe that the goal of mankind is that we should all have more leisure time to visit museums and art galleries whose masterpieces no longer mean anything to us. "Well, maybe the universe is banal!". But if it is, where did we get this overpowering thirst for the sublime and the transcendental?
10) Because of G.K. Chesterton. I think every open-minded agnostic and atheist should read Chesterton's Orthodoxy. They could read it in a day, and it might change their whole view of the universe. It changed mine.