Here Jesus tells his disciples that there are some things they are not ready to hear now, but they will hear them from the Spirit once he had ascended. Since the Spirit proceeds from the Father through the Son, He can grasp what no more human can, and we are bound to give assent to Him, even if we cannot fully understand – it is like Our Lord and Nicodemus, when the latter wondered how a man could be born again. In our regeneration we receive faith, but perfect understanding is not ours. The Spirit, Hilary of Poitiers reminds us, listeth where He will, and He is not beholden to us or required to explain himself. So, in the words of the Creed, we confess we believe in the Father, Son and the Holy Spirit, and we hold firm in that faith. The Infinite is not to be understood fully by the finite, and if we think we fully understand it, then it is not the Infinite Mystery of the Trinity which we grasp but a phantasm of our own devising.
One of those things which the disciple grasped when the Spirit came was that the Spirit was Divine. (St Gregory of Nazianzus).
We are, St Augustine reminds us, to grow in all love, that love which is nurtured in our hearts by the Holy Spirit. It is through the workings of the Spirit that our understanding will become spiritual and surpass the carnal understanding of men. In this life we shall not enter into all truth, but we can be prepared for it. Now we can know only in part, as through a glass darkly, but hereafter we shall know as we are fully known, and we shall see Him face to face. This is what the Lord means when he tells us that the Spirit will guide us into all truth.
St Ambrose comments that the Spirit speaks in the name of the Father and the Son, because they are one God. What the Son said was from the Father, and what the Spirit says is,.likewise from the Father and Son. The Son is biorn of the father, and the Holy Spirit proceeds from the Father, but only the Father, St Augustine reminds us, is ‘not of another’. But we should not therefore think there is any disparity in the Trinity, for the Son and the Spirit are equally one God with the Father. The distinction is that the Son is born of the Father and the Spirit proceeds from the Father through the Son, but that does not make any difference between them as to substance, for they are consubstantial. The Spirit is not inferior to the Father, any more than the Son is, and these errors are heresy and condemned by the Church. This is, of course, extremely hard for us to comprehend, and we see it as through a glass darkly, but since the Church has declared it to us, and the Church is guided by the Spirit, we accept His word in faith.
As St Gregory Nazianzus expresses it:
All things that the Father has are the Son’s. And … all that belongs to the Son is the father’s. Nothing then is peculiar [to any one Person] because all things are in common. For their being itself is common and equal, even though the Son receives it from the Father.