The great Cornelius a Lapide gives an excellent answer!
You ask what is this special supersubstantial, or daily bread. Calvin, and Philip Melancthon, understand it of corporeal food only. Some Catholics understand it to mean only spiritual food. Certainly SS. Jerome, Cyril, Ambrose, Cassian, speak expressly of this alone, in the passages about to be cited. But I say that this bread is both material, for the sustenance of the body, and spiritual and heavenly bread, suitable for the nourishment of the soul, such as the word of God and the Eucharist. We have need of both, and therefore we ought to ask for both, and for the latter so much more earnestly than the former, as the soul is superior to the body. And this is denoted by the word supersubstantial, which S. Jerome explains to mean superexcellent, surpassing all created substances, because, as Cassian says, “the sublimity of its magnificence and its sanctity is superior to that of the whole creation.” And for this reason, in the Greek, the definite article is added, doubled in truth,
τὸν άρτον τὸν ε̉πιούσιον, the bread the supersubstantial. As though it were said, “Give us bread not common, but celestial and divine.” Christ alludes to the manna given to the Hebrews, which was a type of the Eucharist. For of manna, it is said in Ps. lxxviii. 24, “He gave them bread from heaven.” “Man did eat angels’ food.” Thus, therefore, manna was food ε̉πιούσιος, i.e., heavenly and angelic; but much more is the Eucharist. Whence in Wisd. xix. 20, both are called in Greek Ambrosia, which is said by the poets to be the food of the gods. S.Ambrose calls the Eucharist this supersubstantial bread. “If,” he says, “this be daily bread, why do you receive it only once a year? So live that you may be fit to receive it daily.” Thus the first Christians were accustomed to communicate daily, as is plain from Acts ii. 46. And S. Cyprian (de Orat. Domin.) says, “We ask that this bread may be daily given us, lest we, who are in Christ and daily receive the food of the Eucharist, by the intervention of some grave fault, by abstaining and not communicating, should be kept back from the heavenly Bread, and separated from the Body of Christ, when He Himself has admonished us saying, ‘I am the Bread of life, Who came down from Heaven. If any man shall eat of My Bread he shall live for ever.’” (S. John vi.)
Note that under the term bread, by a Hebraism, whatsoever is necessary for food, clothing, habitation, and the life both of the body and the soul, is sought for. “We ask for a sufficiency,” says S. Augustine (Epist. 121). “By the word bread we mean everything.”
