1 Corinthians 3:2

2. I have fed you with milk Here it is asked, whether Paul transformed Christ to suit the diversity of his hearers. I answer, that this refers to the manner and form of his instructions, rather than to the substance of the doctrine. For Christ is at once milk to babes, and strong meat to those that are of full age, (Hebrews 5:13, 14,) the same truth of the gospel is administered to both, but so as to suit their capacity. Hence it is the part of a wise teacher to accommodate himself to the capacity of those whom he has undertaken to instruct, so that in dealing with the weak and ignorant, he begins with first principles, and does not go higher than they are able to follow, (Mark 4:33,) and so that, in short, he drops in his instructions by little and little, lest it should run over, if poured in more abundantly. At the same time, those first principles will contain everything necessary to be known, no less than the farther advanced lessons that are communicated to those that are stronger. On this point read Augustine’s 98th homily on John. This tends to refute the specious pretext of some, who, while they do but mutter out, from fear of danger, something of the gospel in an indistinct manner, pretend to have Paul’s example here. Meanwhile, they present Christ at such a distance, and covered over, besides, with so many disguises, that they constantly keep their followers in destructive ignorance. I shall say nothing of their mixing up many corruptions, their presenting Christ not simply in half, but torn to fragments, their not merely concealing such gross idolatry, but confirming it also by their own example, and, if they have said anything that is good, straightway polluting it with numerous falsehoods. How unlike they are to Paul is sufficiently manifest; for milk is nourishment and not poison, and nourishment that is suitable and useful for bringing up children until they are farther advanced.

For ye were not yet able to bear it That they may not flatter themselves too much on their own discernment, he first of all tells them what he had found among them at the beginning, and then adds, what is still more severe, that the same faults remain among them to this day. For they ought at least, in putting on Christ, to have put off the flesh; and thus we see that Paul complains that the success which his doctrine ought to have had was impeded. For if the hearer does not occasion delay by his slowness, it is the part of a good teacher to be always going up higher, till perfection has been attained.