Loving another stems from the fact that all people were created in the image of God.

Rabbi Akiva says: “You shall love your neighbor as yourself” (Leviticus 19:18); this is a fundamental principle in the Torah. One should not [think to treat his fellow as himself in all ways and] say: Since I was humiliated, let my fellow be humiliated with me; since I was cursed, let my fellow be cursed with me. Rabbi Tanhuma said: If you do act in this way, know whom you are humiliating: [A person created in the image of God, and by extension, God. As the verse states:] “In the likeness of God He made him” (Genesis 5:1). (Bereshit Rabba 24)