18 As the prayer goes forward, we ask and say, “Give us this day our daily bread.” And this may be understood both spiritually and literally, because either way of understanding it is rich in divine usefulness to our salvation. For Christ is the bread of life; and this bread does not belong to all men, but it is ours. And according as we say, “Our Father,” because He is the Father of those who understand and believe; so also we call it “our bread,” because Christ is the bread of those who are in union with His body. And we ask that this bread should be given to us daily, that we who are in Christ, and daily receive the Eucharist for the food of salvation, may not, by the interposition of some heinous sin, by being prevented, as withheld and not communicating, from partaking of the heavenly bread, be separated from Christ's body, as He Himself predicts, and warns, “I am the bread of life which came down from heaven.
If any man eat of my bread, he shall live for ever: and the bread which I will give is my flesh, for the life of the world.” When, therefore, He says, that whoever shall eat of His bread shall live for ever; as it is manifest that those who partake of His body and receive the Eucharist by the right of communion are living, so, on the other hand, we must fear and pray lest any one who, being withheld from communion, is separate from Christ's body should remain at a distance from salvation; as He Himself threatens, and says, “Unless you eat the flesh of the Son of man, and drink His blood, you shall have no life in you.” And therefore we ask that our bread— that is, Christ— may be given to us daily, that we who abide and live in Christ may not depart from His sanctification and body.
Source: The Treatises of Cyprian (New Advent)