I have known of folks who were once adherents of Christianity but who have since turned their backs on the faith, renouncing it altogether. This is referred to as “apostasy.” It has been defined as “the abandonment or renunciation of a religious or political belief or principle,” or as “the formal disaffiliation from, or abandonment or renunciation of a religion by a person”.
While it is sad to see people deny or reject their former Christian faith, the good news is there are no severe consequences for it – at least in this life. Of course one day such people will have to stand before their maker, but for now, they can do as they please.
This is certainly not the case with Muslims who renounce their faith. Islam treats apostasy as a crime to be punished by death. This is just one of the many very real differences between Christianity and Islam. And these are not just some old religious squabbles which have no impact on folks today.