"I will ... be God to you and to your offspring after you."
A Call to Worship
I shall be your God," that is, "In your house I shall set up My worship, and among you and your people I shall be the God who is worshiped, and among your descendants I shall manifest Myself by means of signs and visible marks, by means of miracles and wonders, in order that they may know Me beyond all doubt and may adore and worship Me." . . . To adore God is to go to Him for help when you turn your face toward Him and call upon Him in trouble, when you give thanks for deliverance, when you recall and proclaim His acts of kindness by declaring that He is the Creator, the Benefactor, the Promiser, and the Savior. . . It is necessary to add that this God, who tells us how to worship Him, is the Giver of eternal life. . .. Therefore He is the God of the godly, the God of Abraham, for example, of Isaac, and of Jacob; these are living and are not dead, even though they are dead so far as we are concerned. Therefore with these words, with which He promises to be the God of Abraham, the Lord calls not only Abraham but also all his descendants, yes, even all the Gentiles who believe as faithful Abraham did, to the hope of eternal life. He promises that they will live as long as God Himself lives, that is, forever. As authority for this conviction we have the Son of God Himself, who says: "God is the God of the living" [Matthew 22:32].
"I will make you exceedingly fruitful."
The People of God
Those who are circumcised are given the promise that they are the people of God and that God wants to be their God. This means that they are in the fellowship of the kingdom of God, since they have been justified by the justifying faith which the Lord grants them through His Spirit. If this was brought about with the Jews in the Old Testament through the medium of circumcision, why would God not do the same thing with the Gentiles through the medium of the new covenant of Baptism? The command (Matthew 28:19) pertains to all: "Go therefore and make disciples of all nations, baptizing them . . ." Hence whereas circumcision was commanded only to the descendants of Abraham, Baptism is commanded to all the nations, with the promise of salvation if they believe. But if, by virtue of the promise, Abraham's descendants had the blessing that those circumcised on the eighth day would receive the gift of faith and become the people of God, why would this be denied the nations now united with God through the covenant of Baptism? For the situation of Baptism will not be worse than that of circumcision.
"My covenant is with you, and you shall be the father of a multitude of nations."
Of the Flesh and of the Promise
This is the origin of the chief doctrine of theology: that God is the God of the Jews and of the Gentiles, rich toward all, even at that very time when the Law and circumcision flourished. For other nations heard Abraham, heard the prophets, saw the worship at Jerusalem, and believed that the God of the Jews was the only true God. Meanwhile the Jews alone had this seal of righteousness because of which they were conspicuous among all the nations. And even though the Gentiles were not circumcised, they nevertheless called upon and worshiped the same God who revealed Himself to the Jewish people through circumcision. Therefore we do not slight St. Paul, the best and most learned interpreter of Moses. For concerning this chapter he teaches us that so far Moses has written about the birth of the son Ishmael and a descendant of Abraham according to the flesh but has said that this descendant was born without the promise. For God did not speak to Abraham about the son who would be born of the maid; it was Sarah's plan that Abraham should consort with the maid. . .. But with regard to Isaac the matter is different. He is born as the result of the promise, and the promise is attached to him. When this difference is recognized, it will shed a bright light on this discussion about circumcision.
When Abram was ninety-nine years old the LORD appeared to Abram and said to him, "I am God Almighty; walk before Me, and be blameless."
If blamelessness is required of Abraham before the law of circumcision is given, who does not see or understand that this covenant of circumcision does not bring about blamelessness but that blamelessness by faith is required of man before the establishment of this covenant? . . . Accordingly, the righteousness of faith is inculcated on Abraham before God commands him to be circumcised. Since he is commanded to remain righteous and blameless, as he had begun to be, he was righteous at that time. That the [Hebrew] noun [translated as "blameless"] in this passage is plural—be a man of perfections or of integrities—one can appropriately relate to the fact that there is a twofold righteousness: (1) the perfect righteousness, through which we are righteous before God through faith; (2) the imperfect righteousness, through which we are righteous before God and men so far as our conduct and reputation is concerned.