What does 'to them that perish, foolishness' mean?

In 1 Corinthians 1:18, Paul identifies a clear distinction between responses to the gospel: while believers perceive the preaching of the cross as the very power of God, those who are perishing regard it as foolishness. This reflects a fundamental spiritual condition; those who are spiritually dead cannot comprehend the things of God. The gospel challenges human pride, as it declares that salvation is solely by grace and undermines any personal merit or achievement. This inherent conflict with worldly wisdom leads to a rejection of the gospel by those who depend on their understanding.