Summa contra Gentiles3.119 Chapter CXIX. That our mind is directed to God by certain sensible things

Since it is connatural to man to acquire knowledge through the senses, and since it is most difficult to arise above sensible things, divine providence has appointed sensible things as a reminder to man of things divine, so that thus man’s intention might the more readily be recalled to divine things, not excluding the man whose mind is not equal to the contemplation of divine things in themselves.

For this reason sensible sacrifices were instituted; since man offers these to God, not because God needs them, but that man might be reminded that he must refer both himself and all that is his to God as his end, and as the Creator, Governor and Lord of all.

Again, sensible things are employed for man’s sanctification, in the shape of washings, anointings, meat and drink, and the uttering of sensible words, as signifying to man that he receives intelligible gifts from an external source, and from God whose name is expressed by sensible words.

Moreover man performs certain sensible actions, not to arouse God, but to arouse himself to things divine: such as prostrations, genuflexions, raising of the voice and singing. Such things are not done as though God needed them, for He knows all things, and His will is unchangeable, and He looks at the affection of the heart, and not the mere movement of the body: but we do them for our own sake, that by them our intention may be fixed on God, and our hearts inflamed. At the same time we thereby confess that God is the author of our soul and body, since we employ both soul and body in the worship we give Him.

Hence we must not wonder that heretics who deny that God is the author of our body, decry the offering of this bodily worship to God. Wherein it is clear that they forget that they are men, inasmuch as they deem the presentation of sensible objects to be unnecessary for interior knowledge and affection. For experience shows that by acts of the body the soul is aroused to a certain knowledge or affection. Wherefore it is evidently reasonable that we should employ bodies in order to raise our minds to God.

The offering of these bodily things to God is called the worship (cultus) of God. For we speak of cultivating those things to which we give our thought in the shape of deeds. Now, we give our thought to God in our actions, not indeed that we may be of advantage to Him, as when we cultivate other things by our actions: but because by such actions we advance towards God. And since by internal acts we tend to God directly, therefore properly speaking we worship God by internal acts. Nevertheless external acts also belong to the divine worship, forasmuch as by these acts the mind is raised to God, as we have said.

This divine worship is also called religion: because by these acts man tethers (ligat) himself, as it were, lest he stray from God. Also, because by a kind of natural instinct he feels himself obliged in his own way to show reverence to God, from whom flows His being and every good.

Wherefore religion is called piety. Because by piety we give due honour to those who begot us. Hence it would seem reasonably to belong to piety to honour God the Father of all. For this reason those who are averse to the worship of God are said to be impious.

And since not only is God the cause and source of our being, but also our whole being is in His power, and all that we have we owe to Him, and because of this He is truly our master, that which we do to honour Him is called service. Now, God is Lord not accidentally, as man of his fellow-man, but by nature. Hence we owe service to God otherwise than to a fellow-man, to whom we are subject accidentally, and who wields over things a restricted dominion, that he receives from God. Wherefore the service due to God is called by the special name of latria by the Greeks.