My thoughts on the end scene--spoilers
I have read many, many interpretations of the ending scene. I have my own thoughts on it, just how it struck me, both at the time of seeing it and pondering it after.
Some have said that it likens him to a Jesus figure. I don't agree. There is nothing in the movie that gives indication that he is Jesus, Jesus-like, or anything else in a spiritual sense.
Others have commented that because he is so lucky, he just happens to wander into a shallow area by chance, (like his name, ha ha!), and the proof point is his checking the water...e.g. he would not have to check the water if he was truly walking on it.
I don't buy that either. There is no point for the setup of all that for such a bland explanation, especially for the end of the film. He is checking the water to show us, the audience, that the water is deep--a plot device if you will. If it was shallow there, it would still be shallow a little ways over!
My feeling is he is of course walking on water. How he can do that, or who he really is, is not the point. The point is, that we the viewer, are put into the same predicament that the very characters in the movie find themselves.
During the entire movie, people take just what they see, and make it into what they want it to be. His philosophy for simple gardening as a metaphor for the economy. His basic communication abilities for someone with depth and thoughtfulness of answer. His demeanor mistaken for someone who might be hiding something. His pleasantness for love. His innocence for directness. We laugh along with the situations because we KNOW what the deal is.
At the end, we find that we DON'T know what the deal really is. We made assumptions about Chance right along with everyone else. And we do that in life when we judge others, all day long, every day, without really knowing them or what they are about. We do business with people we don't know, we have friends that if we really knew them, we might not be their friends, we have sex with people we think love us, and we may not really even know them.
So the ending makes us look at us. It is just as plain as that, and I thoroughly enjoyed that curveball!