I do not know what Protestant Christians believe concerning Abraham, but, as for Catholic Christians;
This story begins with the faith of Abraham, the father of those who believe, and also the father of our faith as Christians, one who, through faith, is also our father. The story continues with the blessings granted to the patriarchs, the revelation to Moses and Israel quotes exodus toward the Promised Land. A new stage opens up with the promise of an unending kingship the promise made to David and his descendants. The prophets in turn interpret this history, calling people to repentance and conversion, thus preparing the human hearts to receive the ultimate gift.
Abraham, father of the people of Israel, father of faith, thus becomes the source of blessing, for in him "all the families of the earth shall call themselves blessed " (Genesis 12:3). The task of the Chosen People is, therefore, to make a gift of their God-- the one true God-- to every other people; in reality, as Christians we are the inheritors of their faith in the one God. Our gratitude, therefore, must be extended to our Jewish brothers and sisters who, despite the hardships of their own history, have held on to faith in this God right up to the present, and who witness to it in the sight of those peoples who, lacking knowledge of the one God, "dwell in darkness and in the shadow of death" (Luke 1:79).
When the Church refers to the Jewish covenant with God as irrevocable and eternal it is to the covenant with Abraham.