Summa Theologica

...so that, when sacrificing, we might know that a visible sacrifice is to be offered to no other than to Him whose invisible sacrifice we ourselves ought to be within our hearts.” Others, however, considered that the external cult of latria should not be exhibited to idols as being good or best in itself, but as consonant with common custom, as Augustine (De civ. Dei, lib. VI, cap. 10, at the end) introduces Seneca saying: “We shall worship,” he said, “in such a way that we remember this kind of cult pertains more to custom than to reality;” and (lib. De vera religione, cap. 5, in the beginning) Augustine says, “Religion is not to be sought from philosophers who accepted the same sacred rites with the people, while in their schools they sounded forth diverse and contrary opinions concerning the nature of their gods and the supreme good.” And some heretics also followed this error, asserting that it is not dangerous if someone, caught during a time of persecution, worships idols exteriorly, provided that he retains the faith in his mind. But this appears manifestly false: for since external cult is a sign of internal cult, just as it is a pernicious lie if someone asserts with words the contrary of what he holds in his heart by true faith, so also it is a pernicious falsehood if someone exhibits external cult to someone contrary to what he feels in his mind. Whence Augustine says against Seneca (De civit. Dei, lib. VI, cap. 10, at the end), that “he worshipped idols the more damnable for this reason, that he performed in such a way those things which he did deceitfully, that the people supposed him to be doing them truthfully.”

To the first, therefore, it must be said that neither in the tabernacle or temple of the Old Law, nor even now in the Church, are images instituted so that the cult of latria may be exhibited to them, but for a certain signification; so that through such images, faith regarding the excellence of the angels and saints may be impressed upon and confirmed in the minds of men. It is otherwise, however, regarding the image of Christ, to whom, by reason of His divinity, latria is due, as will be said (part III, quæst. XXV, art. 3).

To the second and third, the answer is evident through those things which have been said (in the body of the article).