Who are the people to whom the preaching of the cross is foolishness?
The preaching of the cross is foolishness to them that perish—those who reject it, ridicule it, and scorn it. In other words, it is not foolishness to those who are saved, but to them that same preaching is the power of God.
Les explains that the preaching of the cross is foolishness to them that perish—those who simply reject it, ridicule it, and scorn it. He contrasts this with the saved, who have believed it, and for whom that preaching becomes the power of God. Les stresses that this is the power of God, just as God opened the Red Sea by His power, and He exercises that power in resurrecting Christ and bringing us out of our deadness in sin and slavery to it. He also cites verse 24: unto them who are called, both Jews and Greeks, Christ the power of God and the wisdom of God, so we must rely upon that power.
For the preaching of the cross is to them that perish foolishness; but unto us which are saved it is the power of God.