I have been involved with Orthodox, Catholic and Protestant Christianity at different points in my life. I left the Catholic church a few months ago, but at times I feel nagging feelings that I'm going to go to hell for leaving.
One thing that keeps coming back to me are the stories of miracles in Catholic (and Orthodox) Christianity. For someone to be declared a saint in the Catholic church, there must be two miracles attributed to that saint's intercession that cannot be explained by science.
One sort of miracle that really gets to me is Eucharistic miracles. The Catholic church (along with the Eastern and Oriental Orthodox churches) teaches that the bread and wine at the Eucharist truly become the body and blood of Christ. Throughout history there have been numerous instances where a consecrated piece of Eucharistic bread has started to bleed, and at least two incidents where the bread has transformed into flesh (and in one the wine transformed into blood). These last two instances have been tested and shown to be real human flesh (one was tested by an atheist who wasn't told about the miracle, as described here).
How would you answer this? This is one of the strongest pieces of evidence nagging at me to return to the Catholic church (despite the problems with the Christian faith such as there being no evidence for the Exodus and differences in Jesus' birth accounts and genealogies between Matthew and Luke).