To whom is the preaching of the cross foolishness, and to whom is it the power of God?
The preaching of the cross is foolishness to those who perish, the unbelieving world, who regard it as amounting to nothing. But to those who are saved, it is the power of God, the power that saves, frees from the shackles of sin, and is released when one believes the gospel.
Les explains that the preaching of the cross is foolishness to them that perish—the unbelieving world—and that it doesn't amount to anything to them. He highlights the little three-letter word “but” that makes all the difference: the world may think the preaching of the cross is foolishness, but to us who are saved, the preaching of the cross is the power of God. It takes the power of God to save us and set us free from the shackles of sin, and that power can never be released from God until we believe the gospel that Christ died, shed His blood, was buried, and rose again. Les also notes he repeats such things purposely for emphasis.