James 5: 19-20
19 Brethren, if any of you do err from the truth, and one convert him;
20 Let him know, that he which converteth the sinner from the error of his way shall save a soul from death, and shall hide a multitude of sins.
Clearly the person who has slipped away is a believer who has fallen into sin - one who is no longer living a life consistant with his beliefs. Christians disagree over whether or nit ist is possible for people to lose their salvation, but all agree that those who move away from their faith are in serious trouble and need to repent. James urges Christians to help backsliders return to God. By taking the initiative, praying for the person, and acting in love, we can meet the person where he is and bring him back to God.
The book of James emphasizes faith in action. Right living is evidence and result of faith. The church must serve with compassion, speak lovingly and truthfully, live in obedience to God's commands, and love one another. The body of believers ought to be an example of heaven on earth, drawing people to Christ through love for God and one another. If we truly believe God's Word, we will live it day by day. God's Word is not merely something we read or think about, but something we do. Belief, faith and trust must have hands and feet - ours!
I think about all the times I have known where someone has left the church and it seems that no one will continue to take the time to talk to that person. I have seen people avoid past church members like the plague. It really saddens me because isn't that the time to reach out and see what is going on in the lives of those brothers and sisters in Christ? I even watched it happen to my own child.. when he left the church he was suddenly ignored and treated like a stranger. It only pushed him further away and now he wants nothing to do with christianity.