What does 1 Corinthians 3:22 mean?
In this and the previous verse, Paul offers an astounding new reason why the Christians in Corinth should not be divided over which Christian teacher they follow, and which ones they don't. Paul is saying, "Why limit yourself to following the teaching of just one human teacher when God has given all these teachers to you as a gift? Why say 'I follow Paul' when God has given to you Apollos and Peter, as well, to learn from?"Then Paul takes this idea to an even more expansive level: All things belong to those who belong to Christ. This includes the service of Christian teachers, yes, but also the world. And life and death. And the present and the future. In other words, why would any believers see themselves as being limited by anything in the world, including life and death and time? Christ is over all of that, and we are in Christ.
The point here is not that all so-called-Christian teaching is equally valuable. Paul has just pointed out that some human efforts won't stand the fires of God's judgment (1 Corinthians 3:12–15). Scripture also clearly warns of the dangers of false teachers (Galatians 1:8–9; 2 Peter 2:1). But when teachers of truth differ only in name, or style, or emphasis, it's counterproductive to bicker about which one deserves more loyalty.
Paul is asking the Corinthian Christians to own the idea that by being in Christ we gain not only salvation but also all that comes with sharing in Christ's inheritance as the Son of God (Romans 8:12–17). Literally nothing that belongs to God is not available to us through Christ.