Brothers and sisters, you should not expect to hear from us what the Lord then refrained from telling His disciples because they were still unable to bear them (Jn 16:12). Instead try to grow in the love that is shed abroad in your hearts by the Holy Spirit who has been given to you (Rom 5:5), so that, fervent in spirit and loving spiritual things, you may be able to know that spiritual light and that spiritual word which carnal men are unable to bear, and this not by any sign appearing to your bodily eyes or by any sound striking on your bodily ears, but by your inward eyesight and hearing.

What is completely unknown cannot be loved. But when what is known in the slightest degree is also loved, that very love enables one to reach a better and fuller knowledge. If, then, you grow in the love which the Holy Spirit spreads abroad in your hearts, “he will teach you all truth” or, as other codices have it, “he will guide you in all truth” (Jn 16:13), which is why it is said, “Lead me in your way, O Lord, and I will walk in your truth” (Ps 85:11). So it will not be from outward teachers that you learn those things which the Lord at that time declined to utter, but you will all be taught by God (Jn 6:45). Thus the very things that you have learned and come to believe from external lessons and sermons ... your minds themselves may have the power to perceive. ...

But, when he says, “He will teach you all truth” or “will guide you into all truth,” I do not think fulfillment is possible in any one's mind in this present life. After all, who while living in this corruptible and soul-oppressing body (Wis 8:25) can know all truth when even the apostle says, “We know in part” (1 Cor 13:9)? It is by the Holy Spirit, of whom we have now received the pledge (2 Cor 1:22) that we shall attain also to that fullness of knowledge of which the same Apostle speaks: “Then we shall know face to face;” and, “Now I know in part, but then shall I know even as I am known” (1 Cor 13: 9, 12). ...

“Be renewed, then, in the spirit of your mind” (Eph 4:23), and “understand what is the will of God, which is good, and acceptable, and perfect” (Rm 12:2), so that, “rooted and grounded in love, you may be able to comprehend, with all the saints, what is the length, and breadth, and height, and depth, even to know the knowledge-surpassing love of Christ, that you may be filled with all the fullness of God” (Eph 3:17-19). It is in this way that the Holy Spirit will teach you all truth, when he shall shed that love ever more and more broadly in your hearts.   (In Ioannem Tr. 96, 4, 5: PL 35, 1875-1876)