John Calvin Commentary 1 Corinthians 1:18

"For the word of the cross is to them that perish foolishness; but unto us who are saved it is the power of God." — 1 Corinthians 1:18 (ASV)

For the preaching of the cross, etc. In this first clause, a concession is made. For as it might quite readily be objected that the gospel is commonly held in contempt if it is presented in so simple and humble a form, Paul willingly concedes this. However, when he adds that it is so in the estimation of them that perish, he implies that their judgment should be disregarded. For who would choose to despise the gospel at the expense of perishing?

This statement, therefore, must be understood in this way: “However the preaching of the cross, having nothing of human wisdom to commend it, is reckoned foolishness by them that perish; in our view, nevertheless, the wisdom of God clearly shines forth in it.”

He indirectly rebukes, however, the distorted judgment of the Corinthians. While they were, by deceptive words, too easily enticed by ambitious teachers, they regarded with disdain an Apostle who was endowed with the power of God for their salvation, simply because he devoted himself to the preaching of Christ.

In what way the preaching of the cross is the power of God for salvation, we have explained in commenting on Romans 1:16.