Matthew 10:7

And going, &c. What the apostles were to preach, is the second thing to be taken notice of in their mission. We here learn what it is, viz. that The kingdom of heaven is at hand. We here behold the great dignity to which the apostles were raised, when sent to preach. For, says St. Chrysostom, they are not sent to announce sensible things, like Moses and the prophets, but something wholly new, and before unheard of. They are not like the prophets, to confine themselves to the preaching of temporal things, their doctrine is wholly heavenly; they are sent to announce the good things of eternity. (St. Thomas Aquinas)