2 Wherefore, as I have already stated, no other is named as God, or is called Lord, except Him who is God and Lord of all, who also said to Moses, “I am that I am. And thus shall you say to the children of Israel: He who is, has sent me unto you;” and His Son Jesus Christ our Lord, who makes those that believe in His name the sons of God. And again, when the Son speaks to Moses, He says, “I have come down to deliver this people.” For it is He who descended and ascended for the salvation of men. Therefore God has been declared through the Son, who is in the Father, and has the Father in Himself — He who is, the Father bearing witness to the Son, and the Son announcing the Father.— As also Esaias says, “I too am witness,” he declares, “says the Lord God, and the Son whom I have chosen, that you may know, and believe, and understand that I am.”
Source: Adversus haereses (New Advent)