1:19 it is written. Paul is quoting here from Isaiah 29:14, with somewhat similar relevant passages in Jeremiah 49:7 and Obadiah 8. The section from this verse through the end of chapter 2 is a sobering indictment of supposed human wisdom, as opposed to true wisdom in Christ (I Corinthians 1:30).

1:21 wisdom knew not God. Human wisdom—whether ancient Greek philosophy or modern evolutionary scientism—has always sought to explain the origin of the world by some means apart from its God and Creator. In the sight of God, this attempt is not true wisdom, true philosophy, or true science, but mere rebellious foolishness (Psalm 14:1; Romans 1:22).

1:21 foolishness of preaching. To the wisdom of the ungodly, “foolish preaching” is preaching the crucifixion of the world’s Creator by His creation.