Love your neighbor as yourself fulfills the law
Paul quotes four commands from the Ten Commandments. He says they are summed up in the command, "Love your neighbor as yourself."
Be indebted to no one, except to one another in love. For he who loves his neighbor has fulfilled the law. The commandments “Do not commit adultery,” “Do not murder,” “Do not steal,” “Do not covet,” and any other commandments, are summed up in this one decree: “Love your neighbor as yourself.” Love does no wrong to its neighbor. Therefore love is the fulfillment of the law.
Exodus 20:13-17 and Deuteronomy 5:17-21 contain the commands against adultery, murder, theft, and coveting. Leviticus 19:18 commands love for one's neighbor. Romans 13:8-10 quotes these commands and says that love does no wrong to a neighbor.