Where did Homer come from?

It never states that he was a soldier in the movie but if you look closely you can see that the shirt he wears often once had an Army rank on it. I guess he is supposed to be an ex-soldier in the film as well.

One of the joys of an artistic work is that people can construct their own backstory. My guess has always been that Homer came from somewhere in the South, and learned to operate heavy machinery in the army. He is clearly no stranger to hard work, and says that he wanted to be an architect, but couldn't afford the schooling.

A soldier with real skill at running construction equipment would have chafed in the racism of the old South in the early 1960s, and, disgusted, he likely hit the road looking for something better. Homer ran across the sisters, and managed to accomplish something great, even if it was just a small triumph. You'll note that he signs his work where only he and God can see it. I always got the feeling that he found a part of himself there, and left a better, more peaceful person, destined for more small successes and a happier life.

Others have suggested he was sent by God. We all are. Maybe that's the message.