What does 1 Corinthians 3:2 mean?

Paul has compared the Corinthian Christians to babies. Despite being saved for some unexplained length of time, they have not matured spiritually. The problem isn't that they are not Christians, nor have they been denied opportunity to grow. These believers have access to the power of the Holy Spirit. They have simply not participated in the process of abandoning their selfish ways, so they can spiritually grow. They could behave as spiritually-empowered believers, but instead they behave as if they were "merely human" (1 Corinthians 3:3).

Paul writes that when he was with them—when they were first saved—he fed them with milk. By this, he means that he taught them the most basic things about God and what it means to be a Christian. As with any newborn, they were only prepared to consume and digest something very basic. Like babies, they began with liquids, milk. By now, however, they should be ready for solid food. Milk is meant to inspire growth into a more mature, more capable creation.

These believers should, by now, be ready for more challenging truths of selflessly walking in Christ and living according to the Spirit. They're still not ready to chew, however. Why is it that the Corinthian Christians have gained so little maturity? Paul holds them responsible for their own lack of growth.