We are not immune from drifting because we often revert back to our humaness - we do not stay rooted in the Word and in God. Drifting away usually does not occur all at once. It take time - slowly allowing things to pull us out of church - things that take our time that should be spent in regular study and worship to God and his Word. The Parable of the Sower shows this perfectly. Where are our roots? In our own works? Other people? Or in God? I think that some Christians drift when they start to think that "We;;, I have made it - this is about all I can do - I have grown as much as I can". This attitude would almost guarantee drifting.