1 From the words of our Lord, where He says, “I have yet many things to say unto you, but you cannot bear them now,” there arose a difficult question, which I recollect to have put off, that it might be handled afterwards at greater leisure, because my last discourse had reached its proper limits, and required to be brought to a close. And now, accordingly, as we have time to redeem our promise, let us take up its discussion as the Lord Himself shall grant us ability, who put it into our heart to make the proposal.
And the question is this: Whether spiritual men have anything in doctrine which they should withhold from the carnal, but declare to the spiritual. For if we shall say, They have not, we shall meet with the reply, What, then, is to be made of the words of the apostle in writing to the Corinthians: “I could not speak unto you as unto spiritual, but as unto carnal. As unto babes in Christ, I have given you milk to drink, and not meat to eat: for hitherto you were not able; neither yet now are you able; for you are yet carnal?” But if we say, They have, we have cause to fear and take heed, lest under such a pretext detestable doctrines be taught in secret, and under the name of spiritual, as things which cannot be understood by the carnal, may seem not only capable of being whitewashed by plausible excuses, but deserving also to be lauded in preaching.
Source: Tractates on the Gospel of John (New Advent)