As then we can expect nothing else on earth than to be subject to the devil, who has the world under his control and is always sowing his tares, our Lord, as the faithful teacher and shepherd of our souls, admonishes us in our text to beware of false prophets.
It is as though He would say: I have given you my Word and have taught you what to do, how to understand the ten commandments, how to trust in God and to call upon Him in prayer, and also how to do good works. Now all depends on your care that ye be not led away from this doctrine. I warn you, and you will have no excuse; for I do not send you among angels, but among wolves, and do not sow you among wheat, but in the midst of tares. Therefore beware, lest you be misled. (Luther’s House Postil, Sermon for the Eighth Sunday after Trinity, Volume 3, p. 727)