An excellent post on salvation from TS. Here's the crucial point:
There's also the pious sentiment that "only God reads hearts, so only He knows who is saved" but I would argue it's exactly the opposite. Only God knows Himself, and so only He knows who is saved. It wouldn't matter if we could read hearts because we wouldn't know where to draw that line between saved and unsaved. It's not heart-reading that matters, but the line between Judgment and Mercy (is there one? or will they 'kiss'?), and only God knows where to draw it. Man would have to know God and man doesn't.
Read the rest too. There were several sections I wanted to quote, for example, the Baptist preacher scenario on salvation.
Oremus pro invicem!