Objection 1. It seems that it does not belong to man alone to eat this sacrament spiritually, but likewise to angels. Because on Psalm 77:25: "Man ate the bread of angels," the gloss says: "that is, the body of Christ, Who is truly the food of angels." But it would not be so unless the angels were to eat Christ spiritually. Therefore the angels eat Christ spiritually.
Objection 2. Further, Augustine (Tract. xxvi in Joan.) says: By "this meat and drink, He would have us to understand the fellowship of His body and members, which is the Church in His predestinated ones." But not only men, but also the holy angels belong to that fellowship. Therefore the holy angels eat of it spiritually.
Objection 3. Further, Augustine in his book De Verbis Domini (Serm. cxlii) says: "Christ is to be eaten spiritually, as He Himself declares: 'He that eateth My flesh and drinketh My blood, abideth in Me, and I in him.'" But this belongs not only to men, but also to the holy angels, in whom Christ dwells by charity, and they in Him. Consequently, it seems that to eat Christ spiritually is not for men only, but also for the angels.
On the contrary, Augustine (Tract. xxvi in Joan.) says: "Eat the bread" of the altar "spiritually; take innocence to the altar." But angels do not approach the altar as for the purpose of taking something therefrom. Therefore the angels do not eat spiritually.
I answer that, Christ Himself is contained in this sacrament, not under His proper species, but under the sacramental species. Consequently there are two ways of eating spiritually. First, as Christ Himself exists under His proper species, and in this way the angels eat Christ spiritually inasmuch as they are united with Him in the enjoyment of perfect charity, and in clear vision (and this is the bread we hope for in heaven), and not by faith, as we are united with Him here.
In another way one may eat Christ spiritually, as He is under the sacramental species, inasmuch as a man believes in Christ, while desiring to receive this sacrament; and this is not merely to eat Christ spiritually, but likewise to eat this sacrament; which does not fall to the lot of the angels. And therefore although the angels feed on Christ spiritually, yet it does not belong to them to eat this sacrament spiritually.
Reply to Objection 1. The receiving of Christ under this sacrament is ordained to the enjoyment of heaven, as to its end, in the same way as the angels enjoy it; and since the means are gauged by the end, hence it is that such eating of Christ whereby we receive Him under this sacrament, is, as it were, derived from that eating whereby the angels enjoy Christ in heaven. Consequently, man is said to eat the "bread of angels," because it belongs to the angels to do so firstly and principally, since they enjoy Him in his proper species; and secondly it belongs to men, who receive Christ under this sacrament.
Reply to Objection 2. Both men and angels belong to the fellowship of His mystical body; men by faith, and angels by manifest vision. But the sacraments are proportioned to faith, through which the truth is seen "through a glass" and "in a dark manner." And therefore, properly speaking, it does not belong to angels, but to men, to eat this sacrament spiritually.
Reply to Objection 3. Christ dwells in men through faith, according to their present state, but He is in the blessed angels by manifest vision. Consequently the comparison does not hold, as stated above (ad 2).
Source: Summa Theologica (New Advent)