What does 1 Corinthians 3:21 mean?

Paul has summed up once more that human wisdom and God's wisdom cannot coexist. Human wisdom unaided by the Spirit, rejects faith in Christ because the human mind is unable to comprehend spiritual truth (1 Corinthians 2:14).

Paul now writes that those who are in Christ should not boast in men. More specifically, Paul has in mind that the Corinthians must stop dividing themselves over their loyalty to one Christian leader over another (1 Corinthians 1:11–12). This way of thinking is based on human wisdom, and it is futile and worthless. It is an attempt to selfishly see themselves as wise in their own eyes by selecting the "better" leader as their own.

Paul now shines a bright light on a truth that should free them from this: All things are yours. In other words, why cut themselves off from any of God's good gifts to them for the sake of pride? God has gifted the Corinthians with good teaching from Paul and Apollos and Peter. They are settling for too little by simply declaring themselves to belong to one teacher or the other. Why not receive the ministry of all three men as their own?