“And one of them, a lawyer, asked him a question, to test him.  ‘Teacher, which is the great commandment in the law?’  And he said to him, ‘You shall love the Lord your God with all your heart, and with all your soul, and with all your mind. This is the great and first commandment. And a second is like it, You shall love your neighbor as yourself. On these two commandments depend all the law and the prophets.’”   (Matthew 22:35-40, RSV.)

The second of these two precepts presupposes that I love myself, but it does not command me to love myself.  There is no need, because everyone loves himself.  Even the suicide desires his own good; he merely makes the mistake of thinking that he would be better off dead.  The moral problem is not that we love ourselves, but that we love ourselves the wrong way.

Thomas Aquinas holds that love of God and love of neighbor “are the first general principles of the natural law, and are self-evident to human reason.”    They are inviolable:  We may not transgress them for the sake of supposedly "greater" ends, like telling lies to elect good men to office.  They are also non-substitutable:  We may not trade them off against each other, like committing a few more murders to achieve a larger reduction in thefts.  In these two senses, neither has priority.

But in another sense, loving God certainly has priority -- it is more grave, more important, as the root is more important than the branch.  Besides, the love of God should be beyond measure, while the love of neighbor should be proportioned to the proper love of self.  To be sure, this is a very high proportion.  If I really loved my neighbor as myself I would die for him.  But my love for God should exceed even that.  Even the principle of justice, “Render to each one his due,” might teach that to us, if only we could gaze steadily upon it -- for if God is truly God, then in the most literal of senses we owe Him everything.

In the context of the Decalogue, love of God is spelled out in the first group of commandments, while love of neighbor is spelled out the second group.  The nature of this “spelling out” is crucial.  It is not that the commandments are deduced from love of God and neighbor; that is not how this works.  Rather, it is in the light of the commandments that we first understand what loving God and neighbor mean.  Once we recognize just what love it is that the commandments spell out, we come to understand them more deeply than we did at first.

A warning:  You may try to be truthful about the goodness of loving your neighbor -- but if you lie to yourself about the God who loved your neighbor into being, then your understanding of all love and every neighbor will be defective.  A more adequate understanding of love and neighbor will be terribly dangerous, because it may make you think of God.