Of the Greek words for love — eros (passionate), philia (friendship), storge (familial), agape (self-giving) — the New Testament chooses agape. It is the love that does not depend on the beauty, merit, or affection of its object.
Agape is what the Christian tradition claims God is. And it is what Jesus is depicted as asking of his followers, including toward their enemies — a demand that has shaped, or failed to shape, two millennia of Christian ethics.