Why does God choose the weak things of the world?
God chooses the weak things of the world to confound the things which are mighty. Not many wise after the flesh, mighty, or noble are called. He prepares instruments like Moses apart from human strength, power, and clout, so His calling and wisdom, not fleshly energy, accomplish His purpose.
Les explains from 1 Corinthians chapter 1, beginning at verse 26, that God's calling does not rest on human wisdom or status: not many wise men after the flesh, not many mighty, not many noble are called. Instead, God chose the foolish things of the world to confound the wise, and the weak things of the world to confound the things which are mighty. Les ties this directly to Moses. When Moses was mighty, had power, and had clout, God could not use him; he 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 40 years to prepare him from God's point of view as an instrument God could use. The lesson is that God's wisdom and calling, not man's fleshly ability, must be the source of the work.
For ye see your calling, brethren, how that not many wise men after the flesh, not many mighty, not many noble, are called: