From CS Lewis's The Screwtape Letters, Screwtape writes to his minion nephew Wormwood:
"But do remember, the only thing that matters is the extent to which you separate the man from the Enemy (God). It does not matter how small the sins are, provided that their cumulative effect is to edge the man away from the Light and out into the Nothing. Murder is no better than cards if cards can do the trick. Indeed, the safest road to Hell is the gradual one--the gentle slope, soft underfoot, without sudden turning, without milestones, without signposts."
I thought this was rather thought-provoking & sadly true... Casting Crowns speaks of this very thing in their song, Slow Fade. (I haven't quite figured out how to post a video directly to my blog, so you'll have to click the link.)
Ephesians 6:12 says,
"For we do not wrestle against flesh and blood, but against principalities, against powers, against the rulers of the darkness of this age, against spiritual hosts of wickedness in the heavenly places."
We are at war, people... with the enemy of our souls...