The monoethnic nature of the Sinaitic covenant can be seen in the following verses in particular:
“Now therefore, if you will indeed obey my voice and keep my covenant, you shall be my treasured possession among all peoples, for all the earth is mine, but you shall be to me a kingdom of priests and a holy nation” (Exod 19:5–6);
“You shall be holy to me; for I, Yahweh, am holy, and have separated you from the peoples, that you should be mine” (Lev 20:26).The Deuteronomic covenant, being an expanded renewal of the Sinaitic covenant, was also exclusively made with Israel:
“For what great nation is there that has a god so near to it as Yahweh our God is to us, whenever we call upon him? And what great nation is there that has statutes and rules so righteous as all this law that I set before you today?” (Deut 4:7–8);
“For you are a people holy to Yahweh your God. Yahweh your God has chosen you out of all the peoples on the face of the earth to be his people, his treasured possession” (Deut 7:6);
“you are a people holy to Yahweh your God. Out of all the peoples on the face of the earth, Yahweh has chosen you to be his treasured possession” (Deut 14:2);
These are the terms of the covenant Yahweh commanded Moses to make with the Israelites in Moab, in addition to the covenant he had made with them at Horeb. Moses summoned all the Israelites and said to them: “... You shall keep the terms of this covenant, and do them, so that you may prosper in everything you do. All of you are standing today before Yahweh your God—your leaders and chief men, your elders and officials, and all the other men of Israel, together with your children and your wives, and the foreigners living in your camps who chop your wood and carry your water—in order to enter into the covenant of Yahweh your God and his oath, to confirm you this day as his people, that he may be your God as he promised you and as he swore to your fathers, Abraham, Isaac and Jacob; and it is not with you alone that I am making this covenant and this oath, but with those who are standing here with us today before Yahweh our God, and also with those who are not here with you today” (Deut 29:1–2, 9–15).Understanding the ethnic particularity of the Mosaic covenant helps us to understand the need in God’s plan of salvation for a new covenant. The Mosaic covenant is “problematic” from the perspective that God’s plan involved bringing blessing to the nations as part of a covenant relationship (Gen 12:3). This is something that the Apostle Paul came to realize. Comparing the monoethnic nature of the Mosaic covenant to the Abrahamic promise in Gen 12:3 led Paul to understand that there had to be, in the purposes of God, a new covenant which would open up the door of righteousness and salvation to the Gentiles, and which would fulfill, subsume, and thereby supercede, the Sinaitic and Deuteronomic covenants that God had made previously with Israel.
Thus Paul contrasted the Abrahamic promise with the Mosaic covenant:
The law [of Moses], introduced 430 years later, does not set aside the covenant previously established by God and thus do away with the promise. For if the inheritance depends on the law, then it no longer depends on the promise; but God in his grace gave it to Abraham through a promise (Gal 3:17–18).Paul also understood that it was through Jesus Christ, as proclaimed in the Christian gospel, that the Abrahamic promise of blessing to the nations had been realized:
Scripture foresaw that God would justify the Gentiles by faith, and announced the gospel in advance to Abraham: “All nations will be blessed through you” (Gal 3:8);
So in Christ Jesus you are all children of God through faith, for all of you who were baptized into Christ have clothed yourselves with Christ. There is neither Jew nor Gentile, neither slave nor free, nor is there male and female, for you are all one in Christ Jesus. If you belong to Christ, then you are Abraham’s seed, and heirs according to the promise (Gal 3:26–29).Or as Paul has written in Eph 2:11–16, 19, concerning how the dividing wall of the law of Moses was “destroyed” through the death of Christ on the cross, thereby allowing Gentiles to be members of God’s covenant people:
Therefore, remember that formerly you who are Gentiles by birth and called “uncircumcised” by those who call themselves “the circumcision”—which is done in the body by human hands—that at that time you were separate from Christ, excluded from citizenship in Israel and foreigners to the covenants of the promise, without hope and without God in the world. But now in Christ Jesus you who once were far away have been brought near by the blood of Christ. For he himself is our peace, who has made the two groups one and has destroyed the barrier, the dividing wall of hostility, by setting aside in his flesh the law [of Moses] with its commands and regulations. His purpose was to create in himself one new humanity out of the two, thus making peace, and in one body to reconcile both of them to God through the cross, by which he put to death their hostility … Consequently, you are no longer foreigners and strangers, but fellow citizens with God’s people and also members of his household.Being limited to one nation, the Mosaic covenant cannot by definition bring salvation to the nations. Only one covenant can: the multiethnic, new covenant in Christ Jesus.