The most damning self-deception is when we imagine we are safe in Christ when we aren't even born again. This deception has become very common because many don't point this out. Paul, Peter, John and James had questions about the status of many of those who claimed to be Christians. Writing to the church in Corinth Paul said they should test themselves to see if they were really 'in the faith' (2Co.13:5). Peter told his readers to verify their own salvation lest they were deceived (2Pe.1:10). John described in his letter various differences between those who were and were not born of God (e.g., 1Jn.3:7-9). James pointed out that those who claimed to have 'faith' but didn't have any fruit to show for their faith were still 'dead' (Ja.2:17).
One of the things Peter points out is that a true Christian will be occupied all the time with Christian living! Whatever we do, we'll be concerned about if it is pleasing to God, according to His will and honouring to Him. Peter uses the words faith, moral excellence, knowledge, self-control, perseverance, godliness, brotherly kindness and love (2Pe.1:5-7), and tells us that a true child of God will be really diligent to cultivate these. In other words, a child of God will be working all the time on such aspects of life. Peter warns people who, by implication, are occupied with life in this world and all its attractions, that they may either have forgotten what Jesus had to pay in order to save them or they may not even be properly children of God (vv.8,9). That's why he asks everyone to make sure how they stand before God (v.10).
The warning James gives is absolutely on the spot for many people now who feel quite safe about themselves because they have 'faith' in Jesus – and "everyone knows that it is faith and not works that can save us"! What James says is that it is possible for us to have a wrong type of faith – which is quite useless because it hasn't resulted in any transformation in the way we live.
Many people are scared of examining their own heart to see if their faith is genuine because they think their fragile faith will get shattered or that they will be giving place to the Devil to disturb them. But isn't that like avoiding going to a doctor because he might tell us some 'bad' news? That bad news can be what will get them final healing! Isn't it better to know now if we have been deceived about our relationship with God than to be told about it at the judgment?