5 As these things are so, beloved, I warn you in the love of Christ to beware of impure seducers and sects of obscene filthiness, whereof the apostle says, “But it is a shame even to speak of those things which are done of them in secret:” lest, when they begin to teach their horrible impurities, which no human ear whatever can bear, they declare them to be the very things whereof the Lord said, “I have yet many things to say unto you, but you cannot bear them now;” and assert that it is the Holy Spirit's agency that makes such impure and detestable things possible to be borne.
The evil things which no human modesty whatever can endure are of one kind, and of quite another are the good things which man's little understanding is unable to bear: the former are wrought in unchaste bodies, the latter are beyond the reach of all bodies; the one is perpetrated in the filthiness of the flesh, the other is scarcely perceivable by the pure mind. “Be therefore renewed in the spirit of your mind,” and “understand what is the will of God, which is good, and acceptable, and perfect;” that, “rooted and grounded in love, you may be able to comprehend, with all saints, what is the length, and breadth, and height, and depth, even to know the love of Christ which passes knowledge, that you may be filled with all the fullness of God.” For in such a way will the Holy Spirit teach you all truth, when He shall shed abroad that love ever more and more largely in your hearts.
Source: Tractates on the Gospel of John (New Advent)