It is thus the will of the Lord that we should cleave to the Word and not suffer ourselves to be led astray. Whatever is in opposition to the Word we are to hate and flee from as from the devil himself. For this reason we should never be secure or fall asleep. And as has been said before, wherever the Word is in its purity, wolves will not stay away, but will surely come. This is to be seen first of all in the Church, then also in the civil government and in the family. Everywhere the wolf will interfere and try to lead us away from the Word and do us harm. The Christian Church has the true and pure Word of God; this the devil hates to see, and therefore introduces all kinds of fanatics who bring in new and strange doctrines concerning Baptism, the Lord’s Supper, and the person of Christ, thereby to confuse and mislead the people. And when such fanatics arise, we wicked and inquisitive people have the bad habit, which sticks to us like the plague, to run after them as soon as we hear their novelties, and fall away from the Word. (Luther’s House Postil, Sermon for the Eighth Sunday after Trinity, Volume 3, p. 727)

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)