Why did God knock Saul down on the road to Damascus?
God knocked Saul down to humble him. He was a big man in Judaism, in the upper echelons, and God could not use him from there. So God put him on the dust of the road to Damascus, making him a nobody with nothing to claim, trembling and asking what the Lord would have him do.
Les explains that Saul of Tarsus was a big man in Judaism, profiting in the Jews religion and in the upper echelons. God could not use him from that position, so He put him on the dust on the road to Damascus, where Saul became a nobody with nothing to claim as worthy. Trembling and astonished, Saul asked, 'Lord, what would you have me to do?' The Lord told him to arise and go into the city, and it would be told him what he must do. Though the Lord could have told him directly, God intended to use another person, Ananias, as the go-between. This same pattern appears with Moses and David: God humbles a person before using them.