James 5:19-20: Brethren, if anyone among you wanders from the truth, and someone turns him back, 20 let him know that he who turns a sinner from the error of his way will save a soul from death and cover a multitude of sins.
Galatians 6:1: Brethren, if a man is overtaken in any trespass, you who are spiritual restore such a one in a spirit of gentleness, considering yourself lest you also be tempted.
These two passages are talking about the same situation. Both of them are generally sympathetic to the sinner (that’s a brother or sister in the faith), saying he ‘wanders from the truth’ or is ‘overtaken in a trespass’ like it wasn’t really his fault. And both, starting with “Brothers”, indicate they’re addressing those who are born-again and members of the Body.
That’s the main difference between the two. Paul’s version is talking about someone who is mature in the faith. The signs of maturity are 1] one who is spiritual; 2] has a spirit of gentleness; and 3] ‘considers himself lest he be tempted’. On the other hand, James’ protagonist is just 1] ‘someone’ who 2] turns a sinner from the error of his way’ and ‘covers a multitude of sins’. Clearly not as mature in his perceptions.
How does this apply to us, right here, right now? We need to be alert to see when people are straying. Though it doesn’t say exactly how we’re supposed to ‘turn ‘em back’, or ‘restore such a one’; but probably we should tell them what they’re doing wrong, ask them to stop; and tell them what they ought to be doing instead. While the Bible gives specific instructions about what to do to confront them, but ‘gentleness’ would indicate we should ‘speak the truth in love’ (persistently when necessary). And don’t give up trying, for the reward for success if great: saving a soul from death and covering a multitude of sins.