Deuteronomy 6:13

Whoever yields assent to the supreme authority of divine Scripture should first examine these words: "The Lord your God shall you adore, and him only shall you serve." In Greek the expression used does not signify the service owed to human masters but that which is offered to God, called latreia. Thus idolatry is rightly condemned because the latreia which is due to the true God alone is offered to idols. It does not say, "You shall adore only the Lord your God," but it says, "And him only shall you serve." It used the word only with "you shall serve," meaning, no doubt, that service which is called latreia. To this service belong temple, sacrifice, priest, and other like attributes.

What is to be said of justice in its relation to God? As the Lord says, "No man can serve two masters," and the apostle rebukes those who serve the creature rather than the Creator, so had it not been said before in the Old Testament: "You shall adore the Lord your God and him only shall you serve"? But what need is there to say more about this here since the Scriptures are full of such texts? Justice then offers this rule of life to the lover we are describing: that he serve with gladness the Lord whom he loves, that is to say, the supreme good, the supreme wisdom, the supreme peace; and with respect to all other things, that he govern those which are subject to him and endeavor to subject all else to the same rule. This rule of life is confirmed, as we have shown, by the authority of both Testaments.

What he says about the Lord: And in his name you will swear, it is not to be taken in the sense that he has commanded to swear, but what he has done is to forbid swearing in the name of another divinity. But, as the Gospel says, it is better not to swear; not because the true oath is bad, but so as not to fall into perjury because of the ease in swearing. For he who swears, can swear not only the true, but also the false. And the one who never swears, walks away from perjury. 13 (Dt 8.2). And you will remember all the way that the Lord your God walked you in the desert to afflict you and prove to you and make known what is in your heart, whether you are going to keep his commandments or not. Here it is more clearly said what in another place is dark, due to the kind of expression that is used: The Lord your God is testing you to know if you love him (Dt 13,3). It is already understood that the author puts "to know" as the equivalent of "to make it known." And this very thing is said here with all clarity: To prove to you and make known what is in your heart. It does not say: «and know»; because, if I said it, you had to understand: "make known". 14 (Dt 9.6). And you will know today that the Lord your God does not give you this splendid land as an inheritance because of your merits, because you are a stiff-necked people. Certainly, these are the ones who did not deserve to perish in the desert, because they did not know how to distinguish between the right and the left. But now it is said of them that they are stiff-necked. Therefore, we must see that these words contain a mystery, not that the merits of these men are extolled. And so, so that nobody thinks that these have become suddenly blameworthy, when shortly before they praised his merits, they are told a little later: Remember; do not forget how much you provoked the Lord your God in the wilderness: From the day you left the land of Egypt until you came to this place, you continued to be unbelieving about the Lord. If some of them were unbelievers, and others faithful and good, neither is the promised land granted to those who can not distinguish between the right and the left, so that we understand it in the sense that they have not offended God. Because their parents, who died, and who were not allowed to enter that land, it is seen that they were also like these, and so also among them there were…