Apostasy can have far-reaching and disastrous effects on an entire congregation’s spiritual health. When false teaching goes unchallenged, it breeds more confusion and draws still more shallow and insincere people into the fold. If not vigorously resisted, apostasy will spread like leaven through seminaries, denominations, missions agencies, and other Christian institutions. False teaching thus attacks the church like a parasite, affecting our corporate testimony, inoculating people against the real truth of the gospel, proliferating false and halfhearted “disciples,” and filling the church with people who are actually unbelievers. By such means, entire churches and denominations have been taken over by apostasy.
– John MacArthur