I am not so sure this is right. It seems scripture says that If, Israel keeps the Sinai covenant, then God will keep for them the Abrahamic covenant.
De 7:12 Wherefore it shall come to pass, if ye hearken to these judgments, and keep, and do them, that the LORD thy God shall keep unto thee the covenant and the mercy which he sware unto thy fathers:
So both Covenants are distinct here. But the part for the fathers in Abrahamic covenant is keeping the circumcision of their household.
As Paul clearly states, the addition of the old covenant DOES NOT ANNUL the covenant made with Abraham as to make the promise void.
Galatians 3:16-18 Now the promises were made to Abraham and to his offspring. It does not say, “And to offsprings,” referring to many, but referring to one, “And to your offspring,” who is Christ.
This is what I mean: the law, which came 430 years afterward, does not annul a covenant previously ratified by God, so as to make the promise void. For if the inheritance comes by the law, it no longer comes by promise; but God gave it to Abraham by a promise.
Paul states that the Abrahamic promises (PLURAL) were made to Abraham and his offspring. The offspring being Christ.
The addition of the old covenant, which was conditional upon Israel's obedience to the law of Moses, does not annul the unconditional promises to Abraham and his offspring, because the offspring is Jesus.
The abrahamic promises are to Abraham's offspring, who is Christ. The old covenant was made with the nation of Israel.
The Mosaic covenant does not have any part for God does it?
It does. IF Israel obeyed the law of Moses, GOd would bless Israel (deuteronomy 28:1-14). IF Israel disobeyed the law of Moses, God would curse Israel (deuteronomy 28:15-68). After the blessings and curses had been poured, IF Israel turned back to God, He would restore them from captivity and return them to the land and cirucmcise their heart (Deuteronomy 30:1-6).
So we see that God does have promises to fulfill in the old covenant agreement, whether it is bestowing blessings or curses on Israel.
So is this old covenant agreement still in effect? Are the conditional promises of the old covenant still in effect?
Israel could not keep its covenant. Therefore God had no part to keep in that covenant.
bingo. And knowing this He prophesied through Jeremiah that He would make a new covenant with the house of Israel and Judah.
Hebrews 8:7-8 For if that first covenant had been faultless, there would have been no occasion to look for a second.For he finds fault with them when he says:
c “Behold, the days are coming, declares the Lord,when I will establish a new covenant with the house of Israel and with the house of Judah,
And this old covenant agreement was taken away and made obsolete.
Hebrews 8:13 In speaking of a new covenant, he makes the first one obsolete. And what is becoming obsolete and growing old is ready to vanish away.
Hebrews 10:9 then he added, “Behold, I have come to do your will.” He does away with the first in order to establish the second.
Well, they are still keeping the Abrahamic covenant in circumcision of their Children.
For what purpose? As Paul reveals, the blessing of Abraham is for both circumcised and uncircumcised, for Abraham's faith was counted as righteousness BEFORE he was circumcised. The purpose of Abraham's circumcision was a seal of the righteousness he had by faith prior to be circumcised, as revealed by Paul, in order that he would be the father of both the circumcised and uncircumcised. Thus becoming the father of many nations.
Romans 4:9-12 Is this blessing then only for the circumcised, or also for the uncircumcised? For we say that faith was counted to Abraham as righteousness. How then was it counted to him? Was it before or after he had been circumcised? It was not after, but before he was circumcised. He received the sign of circumcision as a seal of the righteousness that he had by faith while he was still uncircumcised. The purpose was to make him the father of all who believe without being circumcised, so that righteousness would be counted to them as well, and to make him the father of the circumcised who are not merely circumcised but who also walk in the footsteps of the faith that our father Abraham had before he was circumcised.
Since the promiseS (PLURAL) are to Abraham and his offspring, the offspring being Jesus, the fulfillment of these promises are found in Christ. Thus the everlasting covenant of circumcision with Abraham and his offspring, is with Christ.
Galatians 3:16 Now the promises were made to Abraham and to his offspring. It does not say, “And to offsprings,” referring to many, but referring to one, “And to your offspring,” who is Christ.
Per Paul, Circumcision is only value if you obey the law. Thus we see that circumcision had its value through the Abrahamic promises and the old covenant until Christ, in whom its everlasting fulfillment is found.
Romans 2:25-27 For circumcision indeed is of value if you obey the law, but if you break the law, your circumcision becomes uncircumcision. So, if a man who is uncircumcised keeps the precepts of the law, will not his uncircumcision be regarded
b as circumcision? Then he who is physically
c uncircumcised but keeps the law will condemn you who have the written code
d and circumcision but break the law.
And so because the promises to Abraham and his offspring (Christ) are fulfilled in Christ and the old covenant agreement was taken away and made obsolete for those in Christ, neither circumsion nor uncircumcision count for anything.
Galatians 5:6 For in Christ Jesus neither circumcision nor uncircumcision counts for anything, but only faith working through love.