What does 1 Corinthians 4:6 mean?

Paul continues to mention an issue dividing the Corinthian church. They have separated into factions based on which Christian teacher they follow, and which ones they don't. Put another way, they have made themselves judges of those who minister to them, deciding which is faithful and effective and which is not. If it's enough to make them separate into bickering factions, then such judgment must be strong. The believers of Corinth are giving a great deal of weight to their personal views.

Paul has written in the previous verses that only God is qualified to judge the work of His servants. Humans cannot see into the heart of a person, so the Corinthians must stop pronouncing judgment in this way.

Paul now shows that, for their benefit, he has applied his own teaching to himself and Apollos. He is showing them, by his example, how not to declare themselves judges. This is an important concept. To judge another person, when that is not your role, is an act of pride. We puff ourselves up in arrogance when we decide our vote about who is better is what matters most. In truth, this division among the Corinthians existed because of pride and selfishness. It wasn't because of any meaningful differences between those who served as ministers (Romans 14:1; Titus 3:9; Galatians 1:8–9).

Also crucial, Paul has established an example for how to follow the written word given by God, and not to go beyond it. This is a clear statement of a doctrine referred to as sola scriptura, or "Scripture alone." The believers of Corinth are treating their preferences and opinions as if they were more important than the objective written Word of God. Paul explicitly tells them that their own leaders—men like Paul and Apollos—don't presume to go outside of the bounds of Scripture, and neither should they.

This concept is fundamental to our understanding of doctrine and the Christian life. No other source is as authoritative as the Bible, since it's the unchanging message of God accessible to all people. Feelings, opinions, spiritual experiences, philosophical arguments, and human traditions cannot outweigh the Word of God. That which is not biblical is not true, period.