Jerome

However, the disciples gave to the crowds. And all ate, and were satisfied. The crowds received food from the Lord through the apostles. And they took up the remnants of the twelve baskets full of fragments. Each of the apostles fills his own basket with the remains of the Savior, so that he may either have something to give food to the Gentiles afterwards, or teach from the remnants that the loaves were truly multiplied. …

Commentary on Matthew ↗

Hilary of Poitiers

The loaves were given to the apostles, for through them the gifts of divine grace were to be administered. The crowds were then fed with the five loaves and two fish, and they were satisfied. The leftover fragments of bread and fish, after the people had their fill, amounted to twelve baskets. Thus, by the word of God coming from the teaching of the law and the prophets, the multitude was satisfied; and an abundance of divine power, reserved for the Gentiles from the ministry of the eternal food, was left over for the twelve apostles.

Commentary on Matthew 4.11 ↗

Thomas Aquinas

There follows the fullness of refreshment, and this with respect to two things: with respect to satiety, and with respect to what remained. Hence it is said they all ate and were filled, according to that of Ps. 21:27: the poor shall eat and shall be filled etc. And they took up the leavings, twelve baskets full of fragments. Here the fullness of refreshment is indicated by the abundance of the leavings. But why did the Lord wish the leavings to be gathered? The literal reason is that which Chrysostom gives. …

Commentary on Matthew ↗