Sin is never content. It cannot be contained. Thinking you can keep that one “little” sin as a pet is like trying to chain King Kong or keep you own Jurassic Park in your soul. The chains won’t hold. John Owen put it this way,
Sin aims always at the utmost; every time it raises up to tempt or entice, might it have its own course, it would go out to the utmost sin of its kind. Every unclean thought or glance would be adultery if it could; every covetous desire would be oppression, every thought of unbelief would be atheism, might it grow to its head.
Sin is a food that when you feast on it, it devours you. It creates an appetite for itself that it cannot fill. Lewis captured this with Turkish Delight.
At last the Turkish Delight was all finished and Edmund was looking very hard at the empty box and wishing that she would ask him whether he would like some more. Probably the Queen knew quite well what he was thinking; for she knew, though Edmund did not, that this was enchanted Turkish Delight and that anyone who had once tasted it would want more and more of it, and would even, if they were allowed, go on eating it till they killed themselves. But she did not offer him any more.
Sin is the chugging of poison because it tastes good. When this kind of language is used of sin, what kind of sins pop into your mind. I bet you’re thinking of lust, covetousness, or something of the like. Does Peter’s pride register on the radar? How about his unbelief in Jesus’ words? Do you think lust more toxic than pride? Do you think covetousness more addictive than unbelief in Scripture?
Every son of Adam is an expert make-up artist. Even us guys. Every one of us make the pros at Hollywood look like a 4 year old who got into her mom’s vanity. They start with beauty and add to it. It takes real talent to made sin look “good”. We can even make sin appear so holy and pious. Sin can sound like, “Jesus, I’ll never deny you. Even if I have to die with you.”
Sin is like Sauron’s ring. We’re even tempted that we can use it for good. But sin’s wages are always death. Sin is a cursed sword that cannot be wielded for good save by God alone—and then it is never that God makes good of a sin He commits, for He never sins, but of sin that we commit.
Spiritual pride is God-belittling, and soul-destroying. You cannot wield it to build the kingdom. That sword is too big. Put it down now before you really hurt yourself. A fall of Peter’s magnitude begins with a stumble. Before Peter fell by shamefully denying, he was lifted up in pride, and it was the lifting that led to the falling. Pride is climbing up the high dive to do some impressive acrobatics only to spend the last moments flailing wildly as you realize there is no water in the bottom of the pool. Pride is doing some perfect 10 flips only to splat as a zero on the concrete.
Pride is the sin underlying all sin. It’s aim: to be god. You can’t. Someday you will fall. The higher you climb, the bigger the splat.