The commentators think it is a sign of love, l’shon chibbah (Rashi; Midrash Lekach Tov).
Another Midrash (B’reshit Rabba 66:7) thinks the first “Abraham” is a call to the patriarch himself, and the second is an exhortation to his descendants.
Similarly, when Jacob is addressed twice (Gen. 46:2), and likewise with Moses (Ex. 3:4) and Samuel (I Sam. 3:10), the first name is a call to the individual and the second is a call to his descendants: “There is no generation which does not have the duty of emulating the example of these four great figures”.
With a little imagination we might be able to pinpoint the particular things which these four Biblical figures represent:
• Abraham stands for faith. God calls him more than once to venture out and be a pioneer. Out of faith he finds himself able to climb mountains and change the course of history.
• Jacob represents culture and dignity. His macho brother has a more athletic image but he is brawn, not brain. Jacob shows that the way to survival is through knowledge, wisdom and brain power.
• Moses symbolises courage. He has to stand against Pharaohs and courtiers and other establishments, against Korach and other upstart rivals, even against his own people when they constantly complain. Out of courage he moulds a nation and creates a civilisation.
• Samuel teaches the lesson of listening. When others talk incessantly and think that the more noise the better, Samuel knows that you cannot think unless it is quiet, nor can you hear the voice of God unless you can listen to whispers.
From each of our forebears there is a message we can learn.