Cyril of Alexandria:
“I have yet many things to say unto you, but ye cannot bear them now.
Howbeit when He, the Spirit of truth, is come, He shall guide you into all the truth:
for He shall not speak from Himself; but what things soever He shall hear, these shall He speak;
and He shall declare unto you the things that are to come” (John 16;12-13).
The new instruction of the Gospel message belongs not to those who are not yet moulded by the Spirit into newness of life and knowledge, and they cannot as yet contain the mysteries of the Holy Trinity.
The exposition then of the deeper mysteries of the faith is suitably reserved for the spiritual renovation that was to proceed from the Spirit when the mind of those who believed on Christ would no longer allow them to remain in the obsolete letter of the Law but rather induce their conversion to new doctrines and implant in them thoughts enabling them to see a fair vision of the truth.
And that before the Resurrection of our Saviour Christ from the dead, and before partaking of His Spirit, the disciples were…clinging to the legal dispensation, even though the mystery of Christ was clearly superior to it, one might very readily perceive.
[...] When, by being enriched with the grace that is from above and from heaven, they had their strength renewed, according to the Scripture, and had attained to a better knowledge than before, then we hear them boldly saying: But we have the mind of Christ.
By the Mind of Christ they mean nothing else but the advent of the Holy Spirit into their hearts, revealing unto them in due measure all things whatsoever they ought to know and learn.
When then “He,” that is the Comforter, the Spirit of Truth, is come, He shall guide you into all the truth. See how free from extravagance the expression is: note the soberness of the phrase. For having told them that the Comforter would come unto them, He called Him the Spirit of Truth, that is, His own Spirit. For He is the Truth.
[...] The Spirit of Truth then, He says, will lead you to complete knowledge of the truth. For as having perfect knowledge of the truth, of which He is also the Spirit, He will make no partial revelation of it to those who worship Him, but will rather engraft in their hearts the mystery concerning it in its entirety.
For even if now we know in part, as Paul says, still, though our knowledge be limited, the fair vision of the truth has gleamed upon us entire and undefiled.
As then no man knoweth the things of a man, according to the Scripture, save the spirit of the man which is in him, in the same way, I think, to use the words of Paul,none knoweth the things of God save the Spirit of God which is in Him.
Since He is My Spirit [says Jesus], and as it were My Mind, He will surely speak to you of the things concerning Me.
Cyril of Alexandria (c. 376-444): Commentary on John, Book 10 [on John 16:12-13].
