Some will hear the gospel of God's Sovereign Grace in Christ Jesus and give lip service to it. They will, for one reason or another, (usually to keep peace in their family) attend services and associate themselves with the true church. They may even prefer the message of grace because they think it gives them liberty to sin. For lack of true saving faith, they are unable to enter into spiritual worship or any meaningful fellowship with other believers. Most, in time, will lose whatever motivation they have for coming and eventually give up on the charade. "They went out from us for they were never of us". It will be evident that they believed in vain. The tendency is to say they believed in their head but not in their heart. The truth is they never believed in their head or their heart but as natural liars simply espoused with their lips something they never understood.
Those closest to these poor souls know all too painfully the gross inconsistency between what they say they believe and how they live. They know better than all other believers the inability the false professors have to rejoice in Christ or demonstrate the fruits of the Spirit. The heartfelt desire for the believer in this case is for the spurious faith of their loved one to be exposed so they can see their need for true faith in Christ Jesus. The thought is that if we could show them how inconsistent their life is with true saving faith they will give up on their false security and turn in humble submission to Christ Jesus the Lord.
The problem with that idea is twofold. First, it is the Holy Spirit alone that is able to give repentance and faith to dead sinners. Any attempt we make to expose or manipulate an unbeliever is sure to fail. Second, if we preach to expose abusers of grace all we end up doing is discouraging and defeating true believers. The inconsistencies every true believer has in their struggle between the flesh and the spirit becomes the focus of attention. Trying to shame unbelievers with the law will only serve to cause the true children of God worldly sorrow. It will take away their joy by turning their attention away from the accomplished work of Christ to their own works, or lack thereof.
Anytime the pure and simple gospel is preached there will be abusers of grace. Did the Lord not say there would be tares among the wheat? Did He not also say, not to try to root them out? He knew that in doing so we would damage the wheat. In spite of how men might abuse it, we must remain faithful to preach grace. We should pray for those who are yet strangers to it and trust the Lord to either save them or separate them in His time.