To this God we owe service, which in Greek is called latreia, whether in the various mysteries or in our very selves. For together we are his temple, and individually we are his temples (1 Cor 3:16, 17), because he deigns to dwell in the harmony of all and in individuals. He is not greater in all than in one because he neither increases in bulk nor decreases by being shared. When we lift up our heart to him, our heart is our altar. We propitiate him by our priest, his only Begotten. We slay bloody victims to him when we struggle for his truth to the point of bleeding. We burn the sweetest incense for him when we burn with pious and holy love in his sight. We vow and return his gifts and our very selves. We dedicate and consecrate solemn feasts and appointed days to the memory of his blessings so that their memory does not ungratefully fade as time rolls on. On the altar of our heart we offer a sacrifice of humility and praise burning with the fire of love. In order to see him as he can be seen and to cling to him we are cleansed from every stain of sin and evil desire and we are consecrated in his name. For he is the source of our happiness and the goal of our striving. Choosing him, or rather choosing him again–for we had lost him by our neglect—we move toward him by love so that by reaching him we may rest, happy because made perfect by that goal. For our good, the good about which there is great dispute among philosophers, is nothing other than to cling to him, and it is by embracing him, as it were, that our intellectual soul is filled and made fruitful by true virtues. We are commanded to love him with all our heart, with all our soul, with all our strength. To this good we must be led by those who love us while we also are leading those we love. In this way those two commands on which the entire Law and the prophets depend are fulfilled: “You shall love the Lord your God with all your heart, with all your soul and with all your mind” and “You shall love your neighbor as yourself” (Mt 22:37-40).
For a person to know how to love himself, a goal has been appointed for him to which to refer all that he does if he wishes to be happy. To love oneself is to desire to be happy, and this goal is to cling to God (Ps 72:28). When someone knows how to love himself, what else is commanded when he is commanded to love his neighbor as himself than that as much as possible he bring his neighbor to love God? This is worship of God; this is true religion; this is true piety; this alone is the service owed to God. (De civ. Dei, X, 3; PL 41, 280-281)