Nicene and Post-Nicene Fathers, Ser. II, Vol. XI:
The Works of John Cassian.: Chapter XXI. Of our supersubstantial or daily bread.

Chapter XXI.

Of our supersubstantial or daily bread.

Next: “Give us this day our bread which is ἐπιούσιον,” i.e., “supersubstantial,” which another Evangelist calls “daily.” 1614 The former indicates the quality of its nobility and substance, in virtue of which it is above all p. 395 substances and the loftiness of its grandeur and holiness exceeds all creatures, while the latter intimates the purpose of its use and value. For where it says “daily” it shows that without it we cannot live a spiritual life for a single day. Where it says “today” it shows that it must be received daily and that yesterday’s supply of it is not enough, but at it must be given to us today also in like manner. And our daily need of it suggests to us that we ought at all times to offer up this prayer, because there is no day on which we have no need to strengthen the heart of our inner man, by eating and receiving it, although the expression used, “today” may be taken to apply to his present life, i.e., while we are living in this world supply us with this bread. For we know that it will be given to those who deserve it by Thee hereafter, but we ask that Thou wouldest grant it to us today, because unless it has been vouchsafed to a man to receive it in this life he will never be partaker of it in that.

Footnotes

Here Cassian is relying entirely on Jerome’s revised text of the Latin, which has supersubstantialis  in S. Matt. vi. 11, as the rendering of ἐπιούσιος but translates the same word by quotidianum in the parallel passage in S. Luke xi. 3. It is curious that Cassian should have been thus misled, with his knowledge of Greek, as well as his acquaintance with the old Latin version which has quotidianum in both gospels. Cf. Bishop Lightfoot “On a Fresh Revision of the New Testament,” p. 219.