What does 1 Corinthians 3:3 mean?

At the beginning of this letter, Paul thanked God for His grace for all the Christians in Corinth. God had confirmed their faith in Christ by giving them gifts through the Holy Spirit. Paul was grateful that, because they were in Christ, they would stand blameless before God on the day of the Lord (1 Corinthians 1:4–9). These are saved, born-again people; however, they are not spiritually mature people.

Paul now expresses his great frustration with them, in that they have matured so little in their spiritual lives. They remain on the "milk diet" suited for newborns—for immature, brand-new Christians—and they are not ready for the solid food of deeper truths, or for abundant life in Christ by the power of God's Spirit. They are not living as people indwelt by the Holy Spirit; they are living as if they were "merely human."

Why has this happened? Paul says it plainly: "you are still of the flesh." By this, he means that the Christians in Corinth, despite having power from the Holy Spirit, are still selfishly serving themselves first and foremost. They have access to God's Spirit, and the ability to grow into selfless, Christlike lives, but they have not made any progress.

The first evidence Paul presents of their lack of growth is conflict and jealousy among them. While there will always be some level of friction among every other group of humans, Paul means something more concerning. He is referring to quarreling among the Christians of Corinth, according to personal reports of the representatives of a woman called Chloe (1 Corinthians 1:11).

As Paul will make clear, maturing Christians should begin to function differently from unsaved people, or brand-new born-again believers. Clearly, we must choose to actively participate in this growth. God can work in us through the power of the Holy Spirit, but if we're careless or lazy, we'll remain spiritual infants.