Many believe in the idea that a soul's inhabited a previous body (life) and that the soul will occupy another body once the present body dies -- whether or not there's a waiting period between lives. In such belief, the soul carries the sins from the past life to the next one and must purge these sins somehow.
Depending who you talk to on the topic of reincarnation, there are two secondary beliefs. Some believe that these life cycles occur a specific number of times; by the end of which, we're saved or condemned. At the same time, others are more generous as for them these cycles continue till the soul's purged all its sins (Krishna belief of achieving enlightenment).
This beliefs exist outside a predefined religion as members of a religion might believe or ignore the concept of reincarnation.
If all the latter were true, this could explain why, from the moment we're born, some of us seem to start paying back for sins that we might have done in a previous life. If so, how would our understanding of God be affected? Could God have us been born to merely continue a life that we're not aware of and pay for sins that we can't recall? It'd be a cruel god. Of course, we, as Christians, want and need to believe in a just God. Hence most Christians would see reincarnation as an idea that can't exists within our understanding of Christianity.
There's a little twist in this belief. Some people believe that the next life in human form (most likely, if it were true), but some believe you could return as a lower animal.
On a personal level, I don't know what to think. The idea of reincarnation isn't quite my cup of tea, but at times I wonder if it were true. Who could I've been? Who'd I be in a future life? Note that I refer to coming back in human form and not as a lower animal form. Then again, if I were to come back as a lower animal, I'd rather be a lion or an eagle. Of course, this is just too twisted and not really part of the Christian doctrine.
