In C.S. Lewis' Screwtape Letters, he examines Christian life from the devil's perspective. Screwtape, an expert demon, is giving advice to his nephew Wormwood. He discusses how to tempt people by using certain strategies. Lewis states the danger of falling into "lukewarm" feelings about faith and sin. The devil's advice is to keep humans numb and unaware of the sins that they are doing. For Screwtape says, "Murder is no better than cards if cards can do the trick."
Christians who fall into a feeling of half guilt, are also in danger of steadily moving out into nothing. It is in this nothing that Christians must avoid by staying firm in what's right and just. For once we are numb to our actions, we will gradually start to progress into a whole new level of sin, that at first wouldn't dare be reached.
The dangers of just believing that because we go to church we will be saved is that we cannot go through life just doing the motions of a Christian, we must truly act as a child of God would and should act.