"Put on the whole armour of god, that ye may be able to stand against the wiles of the devil. For we wrestle not against flesh and blood, but against principalities, against powers, against the rulers of the darkness of this world, against spiritual wickedness in high (or heavenly) places. Wherefore take unto you the whole armour of God, that ye may be able to withstand in the evil day, and having done all, to stand. Stand therefore, having your loins girt about with truth....." (Ephesians 6:11-14)
1. Protection from the Damining Nature of False Doctrines.
An abscess in the head can be as deadly as one in the stomach. And a corrupt judgment in foundation truths kills as surely as a rotten heart does.
Many people say a person can be saved in any religion if he just follows the light. It does not matter, they say, what you believe as long as you believe something. But their imagination is making as many roads to heaven as Scripture tells us there are ways to hell. This humanistic rationale may sound good but the end of it does not lead to Christ, who says there is no other way to life but by Him: "I am the way, the truth, and the life" (John 14:6). John declares that anyone who will not hold the one true doctrine of Christ is marked eternally as a lost man. And he who will not take God before he dies, the devil will take as soon as he dies.
No matter how much kindess and logic and religion a man mixes in to corrupt true doctrine, he is an obstinate sinner in God's sight and will receive the same condemnation at Christ's hands as the unrepentant drunkard or murderer. Both stand tied together for hell: "They which do such things shall not inherit the kingdom of God" (Galations 5:21).
If ignorance in fundamentals is damning, surely error in fundamentals is far more deadly. If a pound of sin is enough to press to hell, there is no doubt that a ten-pound weight will do it even faster. Error stands farther away from truth than ignorance does and opposes it more vigorously. Error is ignorance with an unseen guillotine.
A man who does not eat enough will die, but the one who swallows poison will lose his life even sooner. The apostle assures us the "pernicious ways" and "damnable heresies" bring "swift destruction" upon those who accept them (2 Peter 2:1,2). All rivers find their way sooner or later to the sea, but some return with a swift stream and get there before the others. If you want a shorter trip to hell than you could schedule with more conventional sin, then slide into this rushing river of corrupt doctrine and it will not take long for you to get there.
from The Christian in Complete Armour, Vol. 2, by William Gurnall (17th Century Puritan preacher)