John Chrysostom

But when we come to the end, there is a difference. For, "they did all eat," so it is said, "and were filled, and they took up of the broken meat that was left, seven baskets full. And they that did eat were four thousand men, besides women and children." But why at the former time, when there were five thousand, did twelve baskets full remain over and above, whereas here, when there were four thousand, it was seven baskets full? For what purpose, I say, and by what cause, were the remnants less, the guests not being so many? …

Homily on the Gospel of Matthew 53 ↗

Hilary of Poitiers

They brought forward seven loaves of bread. The Gentiles received no salvation from the law and the prophets. However, they live because of the grace of the Spirit whose sevenfold light, as noted by Isaiah, is a gift. Therefore through faith in the Spirit the Gentiles receive salvation. They recline on the ground, for they were not subject to any works of the law or the flesh but were called in their earthly condition to the Spirit of the sevenfold light. …

Commentary on Matthew 15.10 ↗

Thomas Aquinas

Consequently he sets forth the fullness of the refreshment, from the abundance of the remains and from the number of those who ate. And they all ate. Someone could say that from a little bread many can receive, such that each has only a little; but it was not so; rather, they were filled; hence they ate until they were satisfied; Ps. 77:29: they ate and were filled, every one. Likewise, there were many remains, because they took up seven baskets. …

Commentary on Matthew ↗