Preach, saying, &c.— The original word is Κηρυσσετε, which is derived from κηρυξ a herald, and signifies "proclaim, with that ardour and zeal which becomes my heralds." Probably they were to make this proclamation with a loud voice, as they passed through the streets of the towns which they visited, as Jonah declared his message to Nineveh. See Jonah 3:4 and Doddridge.
Related Commentaries of Matthew 10:7
Matthew 10:7
7 And as ye go, preach, saying, The kingdom of heaven is at hand.