The apostles taught Jesus was the true servant, the true son, and the true Israel of God.
Isaiah also spoke of Israel and the descendants of Abraham as the people of god. Through the seed of Abraham that the nations of the earth would be blessed. So, Jesus is also the true seed of Abraham.
7 Know then that it is those of faith who are the sons of Abraham. 8 And the Scripture, foreseeing that God would justify the Gentiles by faith, preached the gospel beforehand to Abraham, saying, “In you shall all the nations be blessed.” Gal 3.
Abraham believed the same gospel Paul preached, And if you are Christ's, then you are Abraham's offspring, heirs according to promise. Gal 3:29.
From the beginning the true children of Abraham, whether Jew or Gentile will be heirs of God's promise. If they are Christ's who is the true seed of Abraham.
8 But you, Israel, my servant,
Jacob, whom I have chosen,
the offspring of Abraham, my friend;
9 you whom I took from the ends of the earth,
and called from its farthest corners,
saying to you, “You are my servant,
I have chosen you and not cast you off”;
10 fear not, for I am with you;
be not dismayed, for I am your God;
I will strengthen you, I will help you,
I will uphold you with my righteous right hand. Isaiah 41.