1. But it is irrational in men who posit one only separate first principle, to pay divine worship to another. For we pay worship to God, not as though He needed it, but to strengthen in ourselves by sensible signs a true opinion about God. Now the opinion that God is one, exalted above all, cannot be strengthened in us by sensible signs except by our paying him some separate and peculiar tribute, which we call divine worship. Evidently then true opinion about the one principle is weakened, if divine worship is paid to several.
2. This exterior worship is necessary for man, to the end that man's soul may conceive a spiritual reverence for God. But custom goes a long way in moving the mind of man: for we are more easily moved to that to which we are accustomed. Now the custom among men is that the honour that is paid to him who holds the highest place in the commonwealth, as to the king or emperor, is paid to none other. Therefore there should be a worship that is paid to none other than the one principle of the universe; and that we call the worship of latria.
3. If the worship of latria is due to another merely because he is superior, and not because he is supreme, it would follow that one man should pay latria to another man, and one angel to another angel, seeing that among men, and also among angels, one is superior to another. And since among men he who is superior on one point is inferior on another, it would follow that men should interchange latria in their mutual dealings, which is absurd.
4. Man ought to pay God something special in recognition of the special benefit of his creation; and that is the worship of latria.
5. Latria means service, and service is due to the master. Now he is properly and truly called master, who lays down to others precepts of conduct, and himself takes a precept of conduct from none: for he who executes the arrangement of a superior is rather minister than master. But God's providence disposes all things to their due actions: hence in Holy Writ the angels and the heavenly bodies are said to minister both to God, whose ordinance they execute, and to us, to whose benefit their actions tend. Therefore the worship of latria, due to the sovereign master, is to be paid only to the sovereign principle of the universe.
6. Among all acts of latria, a unique rank belongs to sacrifice: for genuflections, prostrations and other such marks of honour may be paid even to man, although with another intention than they are paid to God: but no one ever thought to offer sacrifice except to him whom he regarded as God, or affected so to regard. The outward rite of sacrifice represents the inward true sacrifice, whereby the human mind offers itself to God, as to the principle of its creation, the author of its activity, the term of its happiness. Therefore to God alone should man offer sacrifice and the worship of latria, and not to any created spirits whatsoever.
Hence it is said: He shall be slain who offers sacrifice to any gods but to the Lord alone (Exod. xxii, 20): The Lord thy God shalt thou adore, and him only shalt thou serve (Deut. vi, 13). And because it is an undue thing for the worship of latria to be paid to any other than the first principle of all things, and only an evil-minded rational creature will incite others to undue acts; evidently men have been set on to the aforesaid undue worships by the instigation of devils, who have presented themselves to men to be adored in place of God, seeking divine honour. Hence it is said: All the gods of the heathen are devils (Ps. xcv, 5): The things which the heathen sacrifice, they sacrifice to devils, and not to God (1 Cor. x, 20).
3.119 : That by certain Sensible Rites our mind is directed to God
3.121 : That the Divine Law directs man to a Rational Use of Corporeal and Sensible Things