That the Son is Very God, of the Same Substance with the Father. Not Only the Father, But the Trinity, is Affirmed to Be Immortal. All Things are Not from the Father Alone, But Also from the Son. That the Holy Spirit is Very God, Equal with the Father and the Son
13 Similar evidence has been collected also concerning the Holy Spirit, of which those who have discussed the subject before ourselves have most fully availed themselves, that He too is God, and not a creature. But if not a creature, then not only God (for men likewise are called gods), but also very God; and therefore absolutely equal with the Father and the Son, and in the unity of the Trinity consubstantial and co-eternal. But that the Holy Spirit is not a creature is made quite plain by that passage above all others, where we are commanded not to serve the creature, but the Creator; not in the sense in which we are commanded to “serve” one another by love, which is in Greek δουλεύειν, but in that in which God alone is served, which is in Greek λατρεύειν.
From whence they are called idolaters who tender that service to images which is due to God. For it is this service concerning which it is said, “You shall worship the Lord your God, and Him only shall you serve.” For this is found also more distinctly in the Greek Scriptures, which have λατρεύσεις. Now if we are forbidden to serve the creature with such a service, seeing that it is written, “You shall worship the Lord your God, and Him only shall you serve” (and hence, too, the apostle repudiates those who worship and serve the creature more than the Creator), then assuredly the Holy Spirit is not a creature, to whom such a service is paid by all the saints; as says the apostle, “For we are the circumcision, which serve the Spirit of God,” which is in the Greek λατρεύοντες.
For even most Latin copies also have it thus, “We who serve the Spirit of God;” but all Greek ones, or almost all, have it so. Although in some Latin copies we find, not “We worship the Spirit of God,” but, “We worship God in the Spirit.” But let those who err in this case, and refuse to give up to the more weighty authority, tell us whether they find this text also varied in the mss.: “Do you not know that your body is the temple of the Holy Ghost, which is in you, which you have of God?”
Yet what can be more senseless or more profane, than that any one should dare to say that the members of Christ are the temple of one who, in their opinion, is a creature inferior to Christ? For the apostle says in another place, “Your bodies are members of Christ.” But if the members of Christ are also the temple of the Holy Spirit, then the Holy Spirit is not a creature; because we must needs owe to Him, of whom our body is the temple, that service wherewith God only is to be served, which in Greek is called λατρεία. And accordingly the apostle says, “Therefore glorify God in your body.”
Source: On the Holy Trinity (New Advent)