What does the Bible say about foolishness in faith?

In Galatians, Paul openly expresses his astonishment at the Galatian believers for quickly deserting the grace of Christ and embracing a different gospel, which is, in fact, no gospel at all. He refers to them as 'foolish Galatians' not in the sense of lacking intelligence, but as thoughtless or easily manipulated. This underscores the importance of adhering to the core message of the gospel, which is centered on faith in Christ and not a mixture of law and grace. Such foolishness leads believers to reject the sufficiency of Christ's sacrifice, which diminishes the grace that God freely bestows upon His elect.