Hilary of Poitiers

As that first multitude which He fed answers to the people among the Jews that believed; so this is compared to the people of the Gentiles, the number of four thousand denoting an innumerable number of people out of the four quarters of the earth.

Catena Aurea by Aquinas ↗

Thomas Aquinas

There follows the number of those who ate: and they that did eat were four thousand men. Above there were five thousand, because they were given over to the five senses; or on account of the five books of Moses; but here four thousand, on account of the four cardinal virtues, or on account of the four Evangelists. Besides children and women. But why are these excluded? Because the imperfect and the weak are excluded from true doctrine; Eph. 4:13: until we all meet unto a perfect man etc.

Commentary on Matthew ↗