What does 1 Corinthians 2:16 mean?

Paul now quotes from Isaiah 40:13 to sum up his teaching in this section. Paul uses the quote to ask a self-answering question: who understands the Lord's mind? Who teaches the Lord anything?

Of course, no human person teaches God anything. He knows all (Isaiah 55:8–9). Paul's answer to the question confirms and adds a layer to what he has already written. We have the mind of Christ. By that, he seems to mean that, aided by the Holy Spirit, believers have been given access to the thoughts of Christ. We have been given the ability to see what is spiritual and to think what Christ thinks.

It's possible that Paul is also referring to the previous verse in which he wrote that nobody can judge "spiritual people," meaning those given the power to understand and believe God's revelation. Since nobody can teach the Lord anything and we have the mind of Christ—through the Holy Spirit—someone who is not spiritual has no standing to judge someone who is (1 Corinthians 2:14).