5 But some one will say, Have spiritual men nothing in the matter of doctrine, which they are to say nothing about to the carnal, but to speak out upon to the spiritual? If I shall answer, They have not, I shall be immediately met with the words of the Apostle Paul in his Epistle 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;” and with these, “We speak wisdom among them that are perfect;” and with these also, “Comparing spiritual things with spiritual: but the natural man perceives not the things of the Spirit of God; for they are foolishness unto him.” The meaning of all this, in order that these words of the apostle may no longer lead to the hankering after secrets through the profane novelties of verbiage, and that what ought always to be shunned by the spirit and body of the chaste may not be asserted as only unable to be borne by the carnal, we shall, with the Lord's permission, make the subject of dissertation in another discourse, so that for the time we may bring the present to a close.
Source: Tractates on the Gospel of John (New Advent)