Augustine of Hippo

He said not 'old and new,' as He surely would have said had He not preferred to preserve the order of value rather than of time. But the Manichæans while they think they should keep only the new promises of God, remain in the old man of the flesh, and put on newness of error. (Quæst. in Matt. q. …

Catena Aurea by Aquinas ↗

Jerome

Therefore, every learned scribe in the kingdom of heaven is like a master of a household who brings forth from his treasure new and old things. The apostles were instructed, the scribes and notaries of the Savior, who recorded his words and precepts on the tablets of the fleshly heart, in the sacraments of the heavenly kingdoms, and they possessed the wealth of the household, casting forth from their treasure new and old teachings: so that whatever they preached in the Gospel, they would confirm with the voices of the law …

Commentary on Matthew ↗

Gregory the Dialogist

Otherwise; The things old are, that the human race for its sin should suffer in eternal punishment; the things new, that they should be converted and live in the kingdom. First, He brought forward a comparison of the kingdom to a treasure found and a pearl of price; and after that, narrated the punishment of hell in the burning of the wicked, and then concluded with Therefore every Scribe, &c. …

Catena Aurea by Aquinas ↗