1 Corinthians 3:2 (ESV)

2 I fed you with milk, not solid food, for you were not ready for it. And even now you are not yet ready,

The image of infants (as opposed to the spiritually mature) is also found in Ephesians 4:13–14 and in Hebrews 5:12 – 6:2. In the Hebrews passage, the image of milk is used to describe simple, basic teaching.

In our verse, however, milk does not primarily refer to the content of Paul’s teaching. He will address a range of theological and ethical topics in the rest of the letter. Rather, the image of milk probably refers to the way in which Paul has had to teach and treat the Corinthians. He has always had to accommodate himself to their low level of spiritual maturity.

The reason why Paul brings up this problematic side of the Corinthian church’s history is because now, five years later, they are still displaying the same immaturity. Even now, they are not yet ready to be addressed as spiritual people.