What does 1 Corinthians 3:18 mean?

Paul sums up his teaching on wisdom and foolishness from earlier in his letter (1 Corinthians 1:18—2:16). He urges his readers not to deceive themselves. In other words, he is asking the Corinthian Christians to check their assumptions about what is true and what is false.

Specifically, Paul warns of the danger of wanting to be wise "in this age" or wise by the standards of the world in any given era. As he taught earlier, the wisdom of the world is limited to what can be observed with human senses and what can be worked out based on those observations. Human beings have no access to spiritual truths. So, they reject faith in Christ as foolishness, and turn away from His death on the cross as payment for human sin.

Still, even for those who trust in Christ, it is tempting to want to be thought wise by those in our culture, especially those who are respected or powerful. We are drawn to prove we agree with their understanding of the world, so they will give us respect.

Paul warns that we must become fools in the eyes of the world, according to the wisdom of this time and place. The only way to be truly wise is to receive God's wisdom, and that comes only by revelation with the help of His Holy Spirit. God's wisdom leads to vastly different conclusions than human wisdom based on a partial understanding of what is knowable. This does not mean actual ignorance (Psalm 19:1; Romans 1:18–23), but a willingness to follow God's truth even when the ungodly world considers it absurd or unpopular.

Ministers, teachers, pastors, and Christian leaders, especially, must be willing to be foolish according to the world's standards if they hope to lead believers towards the true wisdom of God.