John Chrysostom

When therefore He had caught them, then He begins in their presence to work miracles, by His deeds confirming the words of John concerning Him. And He was continually frequenting their synagogues, even by this instructing them that He was not a sort of adversary of God and deceiver, but that He was come in accordance with the Father. And while frequenting them, He did not preach only, but also showed forth miracles. …

Homily on the Gospel of Matthew 14 ↗

Theophylact of Ohrid

And Jesus went about all Galilee, teaching in their synagogues, and preaching the Gospel of the kingdom. Jesus enters the synagogues of the Hebrews to show that He is not opposed to the law. And healing every disease and every infirmity among the people. He begins with miracles, to give credibility to what He teaches. By "disease" is meant chronic illness, and by "infirmity," a temporary bodily disorder.

Commentary on Matthew ↗

Thomas Aquinas

It is customary among kings that, when the army is gathered, they go to war. In the same way Christ, after gathering an army of apostles, goes forth to fight against the devil with the weapons of preaching, in order to expel him from the world. Hence, here the doctrine and preaching of Christ are treated: first, the preaching is mentioned; secondly, its effect (v. 24). …

Commentary on Matthew ↗

Remigius of Rheims

An example of life for doctors; that they should not be inactive, they are instructed in these words, And Jesus went about. That they should not be acceptors of persons the preachers are instructed in what follows, the whole of Galilee. That they should not go about empty, by the word teaching. That they should seek to benefit not few but many, in what follows, in their synagogues. That they should not preach error nor fable, but sound doctrine, is inculcated in the words, preaching the Gospel of the kingdom. …

Catena Aurea by Aquinas ↗