Drifting usually takes place when we're not paying attention... I've gotta stay focused. Have you ever been driving down the interstate- usually on a long roadtrip- and after having been truckin' along for a while, sleepiness sets in. Or boredom. Or something catches your eye off in the distance. Or you just get lost in thought, your brain is somewhere else. What happens? You drift. It usually takes running over those bumpy things on the shoulder of the road to get your attention again. The same is true for our walk with God. This is why it is important to stay alert, to not allow ourselves to get in a spiritual rut, to avoid the religious rotes we often adopt. There's always the threat that you can drift... It's nothing to be afraid of but we must approach life with the realization that we are BEING saved. We are going through a process always. Knowing this, I have to walk in humility, understanding that I gotta stay in God's face, follow closely, keep from straying, avoid the drift, however you wanna say it.
Sometimes situations overtake us so that we forget what we've heard. Or we encounter that oh-so-fun reality of "my flesh doesn't want to." In other words, there are times that I know better but give into my own desires instead of continuing to be processed. Whatever the case, I must keep from drifting and not forget what I've been told, heard, read, etc. Eyes on the road, hands on the wheel...

Hebrews 2:1