Satan endeavors to corrupt our minds with doctrinal error and so William Gurnall gives us a word of warning and exhortation,
“O beware of this soul-infection, this leprosy of the head. I hope you do not think it needless, for it is the disease of the times. This plague is begun, yea, spreads apace. [There is] not a flock, [not] a congregation hardly, that hath not this scab among them. Paul was a preacher the best of us all may write after, and he presseth this home upon the saints, yea, in the constant course of his preaching it made a piece of his sermon. He sets us preacher also upon this work; ‘Take heed therefore unto yourselves, and to all the flock;—for I know this, that after my departure shall grievous wolves enter;—also of your own selves shall men arise, speaking perverse things,’ Acts 20:28-30; therefore watch. And then he presents his own example, that he hardly made a sermon for several years, but this was part of it, to warn every one night and day with tears. We need not prophesy what impostors may come upon the stage when we go off.
There are too many at present above-board of this gang drawing disciples after them. And if it be our duty to warn you of them, surely it is yours to watch, lest you by any of them be led into temptation in this hour thereof, wherein Satan is let loose in so great a measure to deceive the nation. May you not as easily be soured with this leaven, as the disciples whom Christ bids beware? Are you privileged above those famous churches of Galatia and Corinth, many of which were bewitched with false teachers, and in a manner turned to another gospel? Is Satan grown orthodox, or have his instruments lost their cunning, who hunt for souls? In a word, is there not a sympathy between thy corrupt heart and error? Hast thou not a disposition, which, like the fomes of the earth, makes it natural for these weeds to grow in thy soil? Seest thou not many prostrated by this enemy, who sat upon the mountain of their faith, and thought it should never have been removed?
Surely they would have taken it ill to have been told, ‘you are the men and women that will decry Sabbaths, which now ye count holy; you will turn Pelagians, who now defy the name; you will despise prophecy itself, who now seem so much to honour the prophets; you will throw family duties out of doors, who dare not now go out of doors till you have prayed there.’”