I had a friend once who had lived a violent life. He came to a point before I met him where he had called out to God for help in desperation and had became a born again Christian. He dived in head first and his entire life was consumed with religious fervor. He became well known in his church and in his community. Everything changed for him but eventually he fell into hard times and returned to his old ways. He committed a crime and all of his hope that he was forever changed vanished.
I met him a few years after this when he had lost all hope of returning to his holy ways. He talked about how amazing it had been but he no longer made much effort to find God. He tried a few times to reignite the fire but always quit in frustration when he couldn't get back to where he was. The problem wasn't that he couldn't do what he needed to to be right with God, the problem was that his expectations of what God wanted were off.
Everybody has an idea of what it means to be a Christian. Everybody has an idea of what they think God wants from them and for many people it is an obstacle between them and Gods love. This can be an issue with non-Christians but it can be an even bigger problem with those who have started strong and fallen away. I have fallen into the trap of trying to relive past experiences so I could feel saved. I have also found myself stacking expectations on myself that I assumed God wanted until my expectations become impossible to live up to. Eventually I just quit reading Gods word and praying because everything involved in my faith seems too overwhelming.
I think the best thing people can do is to put the past behind them and start fresh with God. Our guilt and shame can make us feel unworthy but a fresh encounter with Gods love can restart the old fire and remind us of Gods understanding and His true love for us.
Hebrews 4:14 Seeing then that we have a great High Priest who has passed through the heavens, Jesus the Son of God, let us hold fast our confession. 15 For we do not have a High Priest who cannot sympathize with our weaknesses, but was in all points tempted as we are, yet without sin. 16 Let us therefore come boldly to the throne of grace, that we may obtain mercy and find grace to help in time of need.