Matthew 4:23

See here, I. What an industrious preacher Christ was; He went about all Galilee, teaching in their synagogues, and preaching the gospel of the kingdom. Observe, 1. What Christ preached - the gospel of the kingdom. The kingdom of heaven, that is, of grace and glory, is emphatically the kingdom, the kingdom that was now to come; that kingdom which shall survive, as it doth surpass, all the kingdoms of the earth. The gospel is the charter of that kingdom, containing the King's coronation oath, by which he has graciously obliged himself to pardon, protect, and save the subjects of that kingdom; it contains also their oath of allegiance, by which they oblige themselves to observe his statutes and seek his honour; this is the gospel of the kingdom; this Christ was himself the Preacher of, that our faith in it might be confirmed. 2. Where he preached - in the synagogues; not there only, but there chiefly, because those were the places of concourse, where wisdom was to lift up her voice (Pro 1:21); because they were places of concourse for religious worship, and there, it was to be hoped, the minds of the people would be prepared to receive the gospel; and there the scriptures of the Old Testament were read, the exposition of which would easily introduce the gospel of the kingdom. 3. What pains he took in preaching; He went about all Galilee, teaching.

— Matthew Henry's Concise Commentary (public domain)

And Jesus went about all Galilee, teaching in their synagogues--These were houses of local worship. It cannot be proved that they existed before the Babylonish captivity; but as they began to be erected soon after it, probably the idea was suggested by the religious inconveniences to which the captives had been subjected. In our Lord's time, the rule was to have one wherever ten learned men or professed students of the law resided; and they extended to Syria, Asia Minor, Greece, and most places of the dispersion. The larger towns had several, and in Jerusalem the number approached five hundred. In point of officers and mode of worship, the Christian congregations are modelled after the synagogue. and preaching the gospel of the kingdom--proclaiming the glad tidings of the kingdom, and healing all manner of sickness--every disease. and all manner of disease among the people--every complaint. The word means any incipient malady causing "softness."

— Jamieson-Fausset-Brown Commentary (public domain)