City of God by Augustine of Hippo

It is this Good which we are commanded to love with our whole heart, with our whole mind, and with all our strength. It is toward this Good that we should be led by those who love us, and toward this Good we should lead those whom we love. In this way, we fulfill the commandments on which depend the whole Law and the Prophets: 'Thou shalt love the Lord Thy God with thy whole heart, and thy whole soul, and with thy whole mind'; and 'Thou shalt love thy neighbor as thyself.' For, in order that a man might learn how to love himself, a standard was set to regulate all his actions on which his happiness depends. For, to love one's own self is nothing but to wish to be happy, and the standard is union with God. When, therefore, a person who knows how to love himself is bidden to love his neighbor as himself, is he not, in effect, commanded to persuade others, as far as he can, to love God?

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