Sforno on Genesis 15:1/ספורנו על בראשית ט״ו:א׳

1אל תירא אברם, do not worry that the four kings will avenge themselves on you.

2שכרך, not only that, but your reward over and beyond that is so great that your merits have not decreased on account of your success in that battle. You deserve much more reward for having gone to the assistance of your brother, displaying a supreme degree of love for him and for those belonging to him. You have liberated the victims of kidnappers.

3הרבה מאד, both in this world

4 and in the world to come. We have been taught, and recite daily in our prayers, that there are things for which one receives some dividends in this world, whereas the principal comes due in the hereafter. One of the good deeds which qualify for such reward is known as גמילות חסדים, the performing of deeds of loving kindness involving not only one’s checkbook but one’s very body (Peah, 1,1).