The law says, “Hear, O Israel, the Lord your God.” It did not say “speak” but “hear.” Eve fell because she said to the man what she had not heard from the Lord her God. The first word from God says to you, “hear.” .
Such too was the teaching of the law: “Hear, O Israel, the Lord your God is one Lord,” that is, unchangeable, always abiding in unity of power, always the same and not altered by any accession or diminution. Therefore Moses called him one. .
Consider now for a while the passages of Scripture which force us to confess that the Lord is one God, whether we are asked about the Father alone, or the Son alone, or the Holy Spirit alone, or about the Father and the Son and the Holy Spirit together. Certainly it is written, “Hear, O Israel, the Lord your God is one Lord.” Of whom do you think that this is said? If it is said only of the Father, then our Lord Jesus Christ is not God. Why did those words come to Thomas when he touched Christ and cried out, “My Lord and my God,” which Christ did not reprove but approved, saying, “Because you have seen, you have believed”? Letter
That Trinity is one God. Not that Father, Son and Holy Spirit are identically the same. But the Father is Father, the Son is Son, and the Holy Spirit is Holy Spirit, and this Trinity is one God, as it is written: “Hear, O Israel, the Lord your God is one God.”
Therefore, in whatever place you may be, because you know that you have been baptized in the one name of the Father and the Son and the Holy Spirit, according to the rule promulgated by the command of our Savior, retain this rule with your whole heart, from the start and without hesitation: the Father is God, and the Son is God, and the Holy Spirit is God. This means the holy and ineffable Trinity is by nature one God, concerning whom it is said in Deuteronomy, “Hear, O Israel, the Lord your God is one God,” and “You shall adore the Lord your God and him alone shall you serve.” Indeed, … we have said that this one God who alone is true God by nature, is not the Father only, nor the Son only, nor the Holy Spirit only but is at one and the same time Father, Son and Holy Spirit. [Thus] we must be wary that while we say in truth that as the Father, Son, and Holy Spirit are one God, insofar as this is a unity of nature, we dare not say or believe something altogether blasphemous. [Such a bl...
Wherefore [Scripture] says, “The Lord God is one Lord.” By the word Godhead it proclaims too the onlybegotten God and does not divide the unity into a duality so as to call the Father and the Son two gods, although each is called God by holy writers. .
Let us see whether the confession of the apostle Thomas agrees with this teaching of the Evangelist, when he says, “My Lord and my God.” He is therefore his God whom he acknowledges as God. And certainly he was aware that the Lord had said, “Hear, O Israel, the Lord your God is one.” And how did the faith of the apostle become unmindful of the principal commandment, so that he confessed Christ as God, since we are to live in the confession of the one God? The apostle, who perceived the faith of the entire mystery through the power of the resurrection, after he had often heard “I and the Father are one” and “All things that the Father has are mine” and “I in the Father and the Father in me,” now confessed the name of the nature without endangering the faith.
“What then?” one may say. “Were they wronged who lived before his coming?” By no means, for men might then be saved even though they had not confessed Christ. For this was not required of them, but not to worship idols and to know the true God. “For the Lord your God,” it is said, “is one Lord.” Therefore the Maccabees were admired, because for the observance of the law they suffered what they did suffer; and the three children, and many others too among the Jews, having shown forth a very virtuous life and having maintained the standard of this their knowledge, had nothing more required of them. For then it was sufficient for salvation, as I have said already, to know God only, but now it is so no more. There is need also of the knowledge of Christ.