Most people associated with evangelical churches are familiar with the practice of a "revival meeting". In its earliest form these gatherings would last for weeks with sessions scheduled every day. The stated purpose of these meetings was to preach to the lost (unchurched) and simultaneously reinvigorate the church itself (thus the idea of a revival or renewal). The very nature of a revival, the fact that the message was aimed in large part to those already in the church and therefore supposedly saved, was an admission that the normal week to week exercises of the church were not effective in promoting and maintaining Christianity even among its own. Such an admission is troubling indeed for anyone who seriously considers church affiliation as essential to right standing before God. If the local congregation needs reviving, those in charge have apparently been presiding over a corpse.
The "revivals" I have experienced were marked by endless "alter calls" with emotional pleading to both the churched and unchurched to repent and to be certain of their salvation. Again, implied in the concept of revival and the call to church people to repent is the idea that even those in the church are not safe from God's wrath. Apparently at least some church members are mistaken in thinking themselves saved or have slipped back into an unsaved state due to a lack of diligence. As necessary as church membership supposedly is, that membership is no guarantee, so as always with salvation through human effort nothing is as certain as complete uncertainty.