And, behold, the Lord stood beside him [Jacob], and said: "I am the Lord, the God of Abraham your father, and the God of Isaac. The ground on which you are lying I will assign to you and to your offspring."
Midrash Ha-Baur (Rabbi Sa'adia b. David, 15th-century Yemen)
Wasn't Isaac his [Jacob's] father? [Abraham] is called his father on account of his teaching him Torah. This is to teach us that just as a son honors his father, so too a student honors their teacher.
This little midrash carries big significance for us as modern readers. Picking up on the surprising mention of Abraham as Jacob's father, we learn an important lesson about the roles different people can play in our lives. Each of us who has been taught by someone is obliged to honor him/her as we would our parents. And the extension of this teaching is that each of us has the potential to play this important role in someone else's life. No matter our family situation, each of us has a job to do in "parenting" the next generation. We all need to find ways to share our gifts and teach others so that they may lead in the future. In that way our legacies live on regardless of how many children we have, and even if we have none at all.
The extension of this is found at the end of the pasuk. God tells Jacob that he will give the land to his offspring. Of course, we could contort this text to mean that only those who are direct descendants of Jacob have a share in the covenant. However, by understanding Abraham, who is not Jacob's father, to be his father by virtue of teaching him, we create room for all those who wish to join the covenant. The covenant can be entered by learning, and this tradition is beautifully carried on today by Jews by choice, who call themselves in Hebrew ben/bat Avraham Avinu (son/daughter of Abraham our father). Abraham is their father in the sense that in converting they have studied his lessons and joined in his destiny.
May it be our blessing that we all rear students, and remember, Abraham is father to all of us because we have learned from him to be in covenant with God.