I've noticed that people like to rag on Peter. He's such an easy target. He's bold and enthusiastic. He puts his foot in his mouth and falls on his face. This is another one of those passages in which Peter becomes an object of disdain to every preacher who preaches on it. "Once more we see Peter eating humble pie." "Peter's pride gets him in trouble again." "What a dumb, impulsive thing Peter did." Etc. Peter tries to walk on water and seems to be doing well, but when his faith totters and he starts to sink, Jesus grabs hold of him and rebukes him with "Oh, you of little faith, why did you doubt?"
But before you use this passage as an excuse to jump all over Peter for his folly, you have to also acknowledge what a remarkable person he is, how dogged and loyal and eager and naive he is in his love for Jesus. He's like a puppy dog that comes barking and rolling and tumbling at you, then in his eagerness he overshoots his mark so that he has to turn around, scramble and come right back at you again. There's something lovable about that clumsiness, that haplessness. I can't imagine that Jesus despised Peter as much as some of us do. Maybe the reason we enjoy seeing Peter's boldness get him in trouble is that we are hoping that lends some merit to our own cowardice and cold love.
Peter hops out of the boat because he wants to go to Jesus. The disciples are just recovering from the shock of thinking they are seeing a ghost, and when Peter hears Jesus' reassuring voice, "Take courage, it is I. Do not be afraid," his impulse is to run to him. "Lord, if it is you, command me to come to you on the water." I used to think Peter just wanted a chance to take part in the cute little magic trick he saw Jesus performing, but looking at this passage again I don't think it was such a trivial request. Peter says, "if it is you," which means he is still uncertain about whether this is Jesus. Yet if the Lord commanded him to come, Peter knows Jesus would surely give him the ability to meet him safely on the water, then Peter would know that this really was his teacher and friend. Peter is simply hungering for that assurance. He's the "jump out and run to Jesus with open arms" type, not the "wait around for Jesus to make it all the way into the boat before seeing if it's really him" type.
When Peter is focused on Jesus and on his eagerness to be with him, he walks miraculously on the water. But as soon as he takes his eyes off Jesus, noticing the wind, growing anxious about his surroundings, his faith leaks out and he begins to sink. The moment he stops trusting and starts calculating, he's done for. But not quite. Even when his faith fails, Jesus reaches out with his hand and saves him. There are a lot of Christians today who think their faith is what saves them, and when things go wrong they blame weak faith as the cause. But faith is always weak; it totters and shakes the moment we take our eyes off Jesus. It is Jesus who saves you, not your faith. He saves you in spite of your little faith; he saves you from your little faith. If you feel yourself losing a grip on him, you can cry to him to save you from yourself, from all your doubts and folly, and he will reach out a hand to prevent you from sinking.