11 If we ought to advance our argument yet further, and turn our inspection to higher themes, let us contemplate the divine nature of the Holy Spirit specially from the following point of view. In Scripture we find mention of three creations. The first is the evolution from non-being into being. The second is change from the worse to the better. The third is the resurrection of the dead. In these you will find the Holy Ghost cooperating with the Father and the Son.
There is a bringing into existence of the heavens; and what says David? “By the word of the Lord were the heavens made and all the host of them by the breath of His mouth.” Again, man is created through baptism, for “if any man be in Christ he is a new creature.” And why does the Saviour say to the disciples, “Go ye therefore and teach all nations, baptizing them in the name of the Father and of the Son and of the Holy Ghost”? Here too you see the Holy Ghost present with the Father and the Son.
And what would you say also as to the resurrection of the dead when we shall have failed and returned to our dust? Dust we are and unto dust we shall return. And He will send the Holy Ghost and create us and renew the face of the earth. For what the holy Paul calls resurrection David describes as renewal. Let us hear, once more, him who was caught into the third heaven. What does he say? “You are the temple of the Holy Ghost which is in you.” Now every temple is a temple of God, and if we are a temple of the Holy Ghost, then the Holy Ghost is God.
It is also called Solomon's temple, but this is in the sense of his being its builder. And if we are a temple of the Holy Ghost in this sense, then the Holy Ghost is God, for “He that built all things is God.” If we are a temple of one who is worshipped, and who dwells in us, let us confess Him to be God, for you shall worship the Lord your God, and Him only shall you serve. Supposing them to object to the word “God,” let them learn what this word means. God is called Θεὸς either because He placed (τεθεικέναι) all things or because He beholds (Θεᾶσθαι) all things.
If He is called Θεὸς because He “placed” or “beholds” all things, and the Spirit knows all the things of God, as the Spirit in us knows our things, then the Holy Ghost is God. Again, if the sword of the spirit is the word of God, then the Holy Ghost is God, inasmuch as the sword belongs to Him of whom it is also called the word. Is He named the right hand of the Father? For “the right hand of the Lord brings mighty things to pass;” and “your right hand, O Lord, has dashed in pieces the enemy.” But the Holy Ghost is the finger of God, as it is said “if I by the finger of God cast out devils,” of which the version in another Gospel is “if I by the Spirit of God cast out devils.” So the Holy Ghost is of the same nature as the Father and the Son.
Source: Letters (New Advent)