Here one God the Father and one Lord the Son are named with the greatest clarity. This is written still more fully in the Epistle to the Corinthians: "But for us there is one God, the Father, from Whom are all things, and one Lord Jesus Christ, through Whom are all things, and we through Him" (1 Cor 8:6). As the Son does not take away from God the Father the meaning of Lord, although He alone is called Lord, so the Father does not deprive the Son of the meaning of God when the Father alone is called God.
Elsewhere we read: "Know that the Lord Himself is God" (Ps 99:3). Again, in another place: "The Lord your God is one God" (Deut 6:4). Indeed, if, as the Arians think, only God the Father is God, then with the same consistency one may conclude that only Jesus Christ is Lord. Then neither the Father would be Lord, nor the Son God. But God forbid that we should think there is no Godhead in lordship, or no lordship in Godhead.
There is one Lord and one God, because the lordship of the Father and the Son is one Godhead. Therefore faith is also called one, because we believe in the Father, and in the Son, and in the Holy Spirit in the same way. Baptism is one, because we are baptized into the Father, and into the Son, and into the Holy Spirit in the same way. We are immersed three times, that the one mystery of the Holy Trinity may be made manifest. Yet we are not baptized into the names of the Father and of the Son and of the Holy Spirit, but into one name, which is understood as God.
I wonder by what sequence of thought Arius, Macedonius, and Eunomius suspect a difference of nature in one name, in one and the same action, and in one and the same mystery. Their disagreement is united in impiety. Having one and the same foul source in the doctrine that the Son and the Holy Spirit are creatures, they produced different streams of heresy.
"One baptism." These words also have force against Valentinus, who tries to prove that there are two baptisms, and against all heretics. They must know that they have no baptism, but that the one Church of Christ alone is the life-giving source. It can also be called one baptism because, although we are immersed three times on account of the mystery of the Trinity, this is counted as one baptism. The baptism in water, in the Spirit, and in fire is also one and the same. So also is that of which the Lord says: "I have a baptism to be baptized with" (Lk 12:50), and, "You will be baptized with My baptism" (Mk 10:39).
The difference of prepositions in the words, "one God and Father of all, Who is over all and through all and in all," points to a different understanding. God the Father is over all because He is the source of all. The Son is through all because He penetrates all things, transcurrit, and passes through all. The Holy Spirit is in all, because without Him there is nothing.
Yet one must not think that the one God is the Father of absolutely everything, so that the name Father may be assigned even to irrational animals. For ten people, five sons and five slaves, we may equally call Him one Lord and one Father for all ten, horum decem. Yet He is not Father of all and not Master of all in the same way. So also in His words, "one God and Father of all," one must understand that for some He is Father, and for others God.
Zeno with his Stoics has the same teaching about creatures and God. Following him, Virgil also says in the Aeneid, Book 6: "For God passes through all lands and the spaces of the sea," and so forth. Again he says: "From the beginning, spirit nourishes and sustains heaven and earth, the watery plains of the sea, the shining orb of the moon, and the great stars. Mind, poured through the members, moves the whole mass and mingles with the great body."
Some think that what is written by the Apostle, "over all, through all, and in all," should be referred to the Father and the Son and the Holy Spirit. Thus the Father is over all, as Creator of all. The Son is through all, because all things were created through the Son. The Holy Spirit is in all, for He is given to believers, and we are the temple of the Holy Spirit, and the Father and the Son dwell in us.
There is one Lord and one God, because the lordship of the Father and the Son is one Godhead. Therefore faith is also called one, because we believe in the Father and the Son and the Holy Spirit in the same way. Baptism is one, because we are baptized into the Father and the Son and the Holy Spirit in the same way. We are immersed three times, that the one mystery of the Trinity may be made manifest.