40 Moreover by any one who carefully uses his reason it will be found that even at the moment of the expected appearance of the Lord from heaven the Holy Spirit will not, as some suppose, have no functions to discharge: on the contrary, even in the day of His revelation, in which the blessed and only potentate will judge the world in righteousness, the Holy Spirit will be present with Him. For who is so ignorant of the good things prepared by God for them that are worthy, as not to know that the crown of the righteous is the grace of the Spirit, bestowed in more abundant and perfect measure in that day, when spiritual glory shall be distributed to each in proportion as he shall have nobly played the man? For among the glories of the saints are “many mansions” in the Father's house, that is differences of dignities: for as “star differs from star in glory, so also is the resurrection of the dead.” They, then, that were sealed by the Spirit unto the day of redemption, and preserve pure and undiminished the first fruits which they received of the Spirit, are they that shall hear the words “well done thou good and faithful servant; you have been faithful over a few things, I will make you ruler over many things.” In like manner they which have grieved the Holy Spirit by the wickedness of their ways, or have not wrought for Him that gave to them, shall be deprived of what they have received, their grace being transferred to others; or, according to one of the evangelists, they shall even be wholly cut asunder, — the cutting asunder meaning complete separation from the Spirit. The body is not divided, part being delivered to chastisement, and part let off; for when a whole has sinned it were like the old fables, and unworthy of a righteous judge, for only the half to suffer chastisement. Nor is the soul cut in two—that soul the whole of which possesses the sinful affection throughout, and works the wickedness in co-operation with the body. The cutting asunder, as I have observed, is the separation for aye of the soul from the Spirit. For now, although the Spirit does not suffer admixture with the unworthy, He nevertheless does seem in a manner to be present with them that have once been sealed, awaiting the salvation which follows on their conversion; but then He will be wholly cut off from the soul that has defiled His grace. For this reason “In Hell there is none that makes confession; in death none that remembers God,” because the succour of the Spirit is no longer present. How then is it possible to conceive that the judgment is accomplished without the Holy Spirit, wherein the word points out that He is Himself the prize of the righteous, when instead of the earnest is given that which is perfect, and the first condemnation of sinners, when they are deprived of that which they seem to have? But the greatest proof of the conjunction of the Spirit with the Father and the Son is that He is said to have the same relation to God which the spirit in us has to each of us. “For what man” it is said, “knows the things of a man, save the spirit of man which is in him? Even so the things of God knows no man but the Spirit of God.”
On this point I have said enough.
Source: De Spiritu Sancto (New Advent)