I'm an INFJ and highly identify with the idea of being an empath, but from what I've skimmed, my understanding goes much deeper than what the present description has been. There are aspects of my experience which I haven't been able to attribute to mirroring, being empathetic, sensitive, etc. I feel 'vibes' from people as soon as they enter the house, whether or not I can see them or even am aware they are in the house at that moment. This isn't always the case, but I have experienced it if the person has a strong enough 'energy' or whatever you want to call it; I'm honestly not sure what to call it at this point. I used to think I was just getting random waves of inexplicable emotion and blamed it on mental stuff, hormones, whatever. However, after seeing a strong correlation that supported it being caused by something outside of myself I began to rethink it. Note; I'm saying CORRELATION, not causation. It could be caused by something else I have yet to discover, but for now this empathic idea makes quite a bit of sense.
I've not yet discovered exactly what my feelings are on how it works, and I haven't decided which logical explanation fits best (if there even is one that we have yet discovered, I'm very supportive of the idea that there are things beyond which our human logic is capable of understanding... we aren't as smart as we think we are and we do NOT have the ability to understand everything through science. This is coming from someone who relies heavily on science too, so don't think I'm not grounded in rational thought to any extent).
Regardless, there are some things that I learned I must accept as true even if I can't concretely understand how it works. The 'leap of faith' idea is completely unnatural to me. The fact that I accept my empathic traits despite not understanding it on a logical level was not easy, but had to be done. If you experience something, even if it seems to defy logic, its hard to deny its existence.