I thought I would share this from an email I received earlier this week. (I have permission from the sender to post this.)
"My question/concern is regarding "coming back" to the faith, if that's the way you would word it. I've had my skepticism about Christianity, and I've definitely been living in a way that does not exemplify a "Christian life," AND I know I need to change a lot of things, but I don't really understand the whole thing about not being able to come back. Is that just if you completely reject a belief in God? And maybe I'm not doing the right things to "come back." I don't know."
The passage I think you are referring to in talking about "not being able to come back" is found in Hebrews 6:4-6 which reads:
"4It is impossible for those who have once been enlightened, who have tasted the heavenly gift, who have shared in the Holy Spirit, 5who have tasted the goodness of the word of God and the powers of the coming age, 6if they fall away, to be brought back to repentance, because to their loss they are crucifying the Son of God all over again and subjecting him to public disgrace." (NIV)
The writer of Hebrews is talking about someone that has completely rejected God, like you mentioned. This would be someone who knows what it means to walk with and toward Jesus and has made a deliberate decision to turn and head in the opposite direction. The impossibility comes in on our part, not God's. He will not force Himself upon me so it becomes impossible for me to come back to repentance (which literally means to do a 180 and head in the opposite direction) if my heart is not willing.
This also brings to mind the story of the Prodigal Son. It would have been impossible for him to come back if he had not had a change of heart and decided to repent, or travel in the opposite direction he was heading, which brought him back home. I would guess that you are more like the Prodigal Son, as that is the case for the majority of us at times in our relationship with Christ.
I'm not sure if there is a list of the "right" things to do to come back but I can say it requires a change of heart, which it sounds like you are experiencing simply because you were willing to send this email. Confess. Repent. Find a church community and get plugged-in, find a small group to get connected to, make it a priority in your day to spend time in the Word, set aside your desires/wants/needs and love other people and I'm guessing that as you begin to do these things you will find that you haven't strayed as far as you think. Continue to pursue this change in direction and allow Christ to welcome you back!