(J. C. Ryle, "Pharisees and Sadducees")
"Watch out for false prophets! They come to you in sheep's clothing, but inwardly they are ferocious wolves!" Matthew 7:15
"For such men are false apostles, deceitful workmen, masquerading as apostles of Christ. And no wonder, for Satan himself masquerades as an angel of light!" 2 Corinthians 11:13-14
False doctrine does not meet us face to face, and proclaim that it is false. It does not blow a trumpet before it, and endeavor openly to turn us away from the truth as it is in Jesus. It does not come before us in broad day, and summon us to surrender. It approaches us secretly, quietly, insidiously, plausibly, and in such a way as to disarm our suspicion, and throw us off our guard. It is the wolf in sheep's clothing, and Satan in the garb of an angel of light—who have always proved the most dangerous foes of the church of Christ.
Let us be on our guard against the "insidiousness" of false doctrine. Like the fruit of which Eve and Adam ate—at first sight it looks pleasant and good, and a thing to be desired. "Poison" is not written upon it, and so people are not afraid. Like counterfeit coin, it is not stamped "bad." It passes for the real thing, because of the very likeness it bears to the truth.
Let us be on our guard against the "very small beginnings" of false doctrine. Every heresy began at one time, with some little departure from the truth. There is only "a little seed of error" needed to create "a great tree of heresy!" It is the little stones, which make up the mighty building. It was the little pieces of lumber, which made the great ark that carried Noah and his family over a deluged world. It is the little leaven, which infiltrated the whole lump. It is the little flaw in one link of the chain cable, which wrecks the gallant ship, and drowns the crew. It is the omission or addition of one little item in the doctor's prescription, which spoils the whole medicine, and turns it into poison!
Let us never allow a little false doctrine to ruin us, by thinking it is "but a little one," and can do us no harm.
There are three things which we never ought to trifle with:
a little poison,
a little sin, and
a little false doctrine.
Let us read the Bible regularly, daily, and with fervent prayer. Let us receive nothing, believe nothing, follow nothing—which is not in the Bible. Let our rule of faith, our touchstone of all teaching—be the written Word of God. "To the law and to the testimony! If they do not speak according to this Word, it is because there is no light in them." Isaiah 8:20