Paul writes with sadness that he couldn't address the fellowship in Corinth as he would have liked. There attentions were still towards the worldly and they were still full of selfish ambition. Milk is a vital component of life-giving strength and health to the baby, but when he or she begins to eat solid food then there is much greater growth and sustainability. Nobody spent their whole life only drinking milk! I recall one boy that I knew from a youth group I led who would only eat sausages and chips and that was affecting his growth! So, Paul is stating that the new convert should be encouraged fairly early on to move from milk to solids in terms of discipleship training and preaching. For the new believer, that entails seeking God as the main focus in life and for the teacher, an understanding of what would be edible at these early stages in their development. I have met Christians who have believed in Jesus for many years, but still appear happy with sipping at milk. They don't want anything which might challenge them, any teaching which might affect their contentment, any greater understanding of the mystery of God because it may give them a headache! Paul thus asserts in this passage that he could tell what a person's relationship with God was by looking at their relationships with their fellow men and women. If that person is argumentative, divisive, trouble-making, then whatever his or her position in church they are not a man or woman of God. As Jesus stated, the definitive demonstration that a person is a lover of God is his or her love of God. Paul goes on to state that God in His grace may choose humans to bring to other humans the message of His love; but it is He alone who wakes their hearts to new life. God only can produce rebirth.