Have you ever been frustrated over people who come to church just to warm pews? It's so easy to point, "Sinner!" - turn your nose up, look other way, and exclude them in fellowship. It takes love of Christ to look inside and see their need.
They didn't give up on God. Otherwise, they wouldn't even be in church. What they may have given up on is either themselves or other Christians.
Maybe they fell. Maybe they were nearly stoned to death by brethren. Perhaps their anger got best of them. It could be that they were falsely accused. They may have misunderstood God's leading, thereby being tricked by Satan.
But, whatever is was, something very painful happened. Satan convinced them God wouldn't receive them, it could happen again, or they don't have strength to begin anew.
Perhaps we could love them best by telling them they ‘can’, that God made a very special provision to help His children with such a need … that when we follow God every step of way, we can't fall (II Ch. 15:2b), that we "can" place of confidence in Him.
A second group of pew warmers, phlegmatic in personality, often have gift of helps. Once they scurried all over God's house, doing countless unnoticed deeds ... until they joined a legalistic church.
If they have to measure up to serve their God, they'll sit there ‘til cows come home. They don't care if you call them dirty names, like ‘Back Slider’. They know who they are, a lot healthier than some of us.
We're not going to see them move, unless it's out door, until our hearts are ready to receive them as already valuable members.