1 Corinthians 3:21 (ESV)

21 So let no one boast in men. For all things are yours,

Paul comes to the same conclusion as in 1 Corinthians 1:31. If human wisdom is folly in the eyes of God (1 Corinthians 3:19), then no believer should boast in men. Paul also provides another support for this conclusion, namely, that all things are yours. Because the Corinthians already possess all things, there is no need for rivalry and partisanship among them.

Stoic philosophers were fond of saying that all things belong to the wise. Paul may be alluding to this idea, but applying it to believers, since they are the truly wise! Not only is there no need for rivalry and partisanship; there is also no need for comparing themselves with the wise people of this world.