Backsliding also known as falling away. You can say like Adam fallen from Glory (Romans 3:23). Hence, backsliding believers also fall down from Glory, Anointing or New Covenant. 

     James 5:19-20 says " Brethren, if any of you do err from the truth, and one convert him. 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". That means we should not only pray for people who are coming to Church but also who left the Church. We should also meat them and counsel them because doing this you will not only save one soul but also cover multitude of Sins. 

     And You will able to forgive someone's sin like our Lord Jesus Christ. You will become His/Her Deliverer or Redeemer. God of Heaven Bless You Abundantly.