The Abrahamic covenant was the covenant that God made with Abraham:

Genesis 12:1-3 (NKJV) Promises to Abram:

12 Now the Lord had said to Abram: “Get out of your country, From your family
And from your father’s house, To a land that I will show you.

2 I will make you a great nation; I will bless you And make your name great;
And you shall be a blessing.

3 I will bless those who bless you, And I will curse him who curses you; And in you all the families of the earth shall be blessed.”

Through this covenant, Abraham is established by God as the father of many nations.

Genesis 22:2 Abraham’s obedience establishes God’s covenant:

Then He said, “Take now your son, your only son Isaac, whom you love, and go to the land of Moriah, and offer him there as a burnt offering on one of the mountains of which I shall tell you.”

Genesis 22:16-18 (NKJV)

16 and said: “By Myself I have sworn, says the Lord, because you have done this thing, and have not withheld your son, your only son—

17 blessing I will bless you, and multiplying I will multiply your descendants as the stars of the heaven and as the sand which is on the seashore; and your descendants shall possess the gate of their enemies.

Genesis 22:18
In your seed all the nations of the earth shall be blessed, because you have obeyed My voice.”

Genesis 26:4: You descendants will multiply like the stars in heaven:

And I will make your descendants multiply as the stars of heaven; I will give to your descendants all these lands; and in your seed all the nations of the earth shall be blessed;

Even those who believe in the death and resurrection of the Messiah, they also are blessed through Abraham’s obedience:

Galatians 3:8
And the Scripture, foreseeing that God would justify the Gentiles by faith, preached the gospel to Abraham beforehand, saying, “In you all the nations shall be blessed.”