Albert Barnes Commentary Matthew 9:35

"And Jesus went about all the cities and the villages, teaching in their synagogues, and preaching the gospel of the kingdom, and healing all manner of disease and all manner of sickness." — Matthew 9:35 (ASV)

The Gospel of the kingdom. That is, the good news of the reign of God, or the good news of the advent and reign of the Messiah (Matthew 3:2).