Adam Clarke on 1 Corinthians 3:2

I have fed you with milk - I have instructed you in the elements of Christianity - in its simplest and easiest truths; because from the low state of your minds in religious knowledge, you were incapable of comprehending the higher truths of the Gospel: and in this state you will still continue. The apostle thus exposes to them the absurdity of their conduct in pretending to judge between preacher and preacher, while they had but a very partial acquaintance even with the first principles of Christianity.