Why couldn't God use Moses when Moses had power and clout?
Scripture teaches that God chose the foolish and weak things of the world to confound the wise and mighty, so He could not use Moses while Moses relied on his own power and clout. Moses acted in the energy of the flesh, thinking he could deliver Israel himself; God therefore had to prepare him forty years in the desert.
Les explains from 1 Corinthians 1:26-27 that not many wise men after the flesh, not many mighty, not many noble, are called; God instead chooses the foolish and weak things to confound the wise and mighty. He connects this directly to Moses: while Moses was mighty, had power, and had clout, God couldn't use him. Moses went out in the energy of the flesh and thought he could deliver the children of Israel. So God put him on the backside of the desert for forty years to prepare him from God's point of view as an instrument He could use.