John Chrysostom

"In calling it new" (he says), "He hath made the first old: but that which decayeth and waxeth old is ready to vanish away." See what was hidden, how he hath laid open the very mind of the prophet! He honored the law, and was not willing to call it "old" in express terms: but nevertheless, this he did call it. For if the former had been new, he would not have called this which came afterwards "new" also. …

Homily on Hebrews 14 ↗

Theophylact of Ohrid

He explains the prophetic expression and says that the very fact that he called this covenant entirely new serves as an indication that the first one ultimately turns out to be old. Having received confidence from the prophet, he finally touches upon the law, showing that our covenant now flourishes. …

Commentary on Hebrews ↗

Oecumenius

"In speaking of a new covenant." For to call it altogether new has made the first covenant old. "And what is becoming obsolete and growing old is ready to vanish away." Now, having taken boldness from the prophet, he himself declares. This, he says, is new, but that one is old. The old is being abolished, he says. Therefore, it has been cast out and dissolved because of old age; as if he were saying: The new has not suddenly ceased the old, but because of its old age and antiquity, that is, because of its weakness and uselessness. …

The Pseudo-Oecumenian Catena on Hebrews ↗

Thomas Aquinas

412. – Then when he says, in speaking of a new covenant, he argues as though from an authority he cited. And he forms this argument: A new is said only in relation to an old. But whatever is called old is, as it were, close to cessation. Therefore, in speaking of a new covenant, he treats the first as obsolete, i.e., it gives us to understand that the former is old. And what is becoming obsolete and growing old is ready to vanish away. …

Commentary on Hebrews ↗