Thou shalt love thy neighbor as thyself. God is to be loved above everything—above all angels, or men, or any created thing. But after God, amongst created things, our neighbor is above all to be loved.
And we are to extend to our neighbor that kind of love with which we love ourselves. Our love of ourselves is not a frigid love, but a sincere and ardent love. In like manner we should love our neighbour, and desire for him all those good things both for the body and for the soul that we desire for ourselves.
This is what our Lord himself teaches us. "All things whatsoever ye would that men should do to you, even so do unto them." There is none other commandment greater than these. St. Matthew (Matthew 22:40) says, "On these two commandments hang the whole Law and the prophets."
There is no commandment greater than these, because all the precepts of the Divine Law are included in them. So that our Lord here teaches us that we ought continually to have these two precepts in our minds and before our eyes, and direct all our thoughts and words and actions by them, and regulate our whole life according to them.