58 This is the bread that came down from heaven. . . .
Augustine: That we who cannot obtain eternal life of ourselves, might live by the eating that bread, He descended from heaven.
Theophylact: We do not eat God simply, God being impalpable and incorporeal; nor again, the flesh of man simply, which would not profit us. But God having taken flesh into union with Himself; that flesh is quickening. Not that it has changed its own for the Divine nature; but, just as heated iron remains iron, with the action of the heat in it; so our Lord’s flesh is quickening, as being the flesh of the Word of God.
58 . . . Not as your fathers did eat manna, and are dead. He that eateth this bread, shall live for ever.
Bede:. To show the wide interval between the shadow and the light, the type and the reality.
Augustine: Even those who eat Christ are subject to natural death; but they live for ever, because Christ is everlasting life.
Chrysostom: If it was possible without harvest or fruit of the earth, or any such thing, to preserve the lives of the Israelites of old for forty years, much more will He be able to do this with that spiritual food, of which the manna is the type. He knew how precious a thing life was in men’s eyes, and therefore repeats His promise of life often; just as the Old Testament had done [Exod 20:12; Deut 22:7; 1 Kgs 3:14; Ps 21:4; Ps 91:16; Prov 3:2]; only that it only offered length of life, He life without end. This promise was an abolition of that sentence of death, which sin had brought upon us.
Scripture from the Douay-Rheims Bible. Commentary from St. Thomas Aquinas, Catena Aurea, Vol. IV (London: Rivington, 1845).