Objection 1. It would seem that the Mother of God is to be worshiped with the adoration of "latria." For it seems that the same honor is due to the king's mother as to the king: whence it is written (1 Kings 2:19) that "a throne was set for the king's mother, and she sat on His right hand." Moreover, Augustine [Sermon on the Assumption, work of an anonymous author] says: "It is right that the throne of God, the resting-place of the Lord of Heaven, the abode of Christ, should be there where He is Himself." But Christ is worshiped with the adoration of "latria." Therefore His Mother also should be.
Objection 2. Further, Damascene says (De Fide Orth. iv, 16): "The honor of the Mother reflects on the Son." But the Son is worshiped with the adoration of "latria." Therefore the Mother also.
Objection 3. Further, Christ's Mother is more akin to Him than the cross. But the cross is worshiped with the adoration of "latria." Therefore also His Mother is to be worshiped with the same adoration.
On the contrary, The Mother of God is a mere creature. Therefore the worship of "latria" is not due to her.
I answer that, Since "latria" is due to God alone, it is not due to a creature so far as we venerate a creature for its own sake. For though insensible creatures are not capable of being venerated for their own sake, yet the rational creature is capable of being venerated for its own sake. Consequently the worship of "latria" is not due to any mere rational creature for its own sake. Since, therefore, the Blessed Virgin is a mere rational creature, the worship of "latria" is not due to her, but only that of "dulia": but in a higher degree than to other creatures, inasmuch as she is the Mother of God. For this reason we say that not any kind of "dulia" is due to her, but "hyperdulia."
Reply to Objection 1. The honor due to the king's mother is not equal to the honor which is due to the king: but is somewhat like it, by reason of a certain excellence on her part. This is what is meant by the authorities quoted.
Reply to Objection 2. The honor given to the Mother reflects on her Son, because the Mother is to be honored for herSon's sake. But not in the same way as honor given to an image reflects on its exemplar: because the image itself, considered as a thing, is not to be venerated in any way at all.
Reply to Objection 3. The cross, considered in itself, is not an object of veneration, as stated above (4,5). But the Blessed Virgin is in herself an object of veneration. Hence there is no comparison.
Source: Summa Theologica (New Advent)