When G-d drove Adam from Paradise, he retained part of his soul to remain there. On Shabbos, G-d releases that part and gives it back to man. This is our extra soul of Shabbos. On this day we are given the opportunity to return to Paradise. The question is asked, where would Adam have gone on Shabbos if he had not been driven out of Paradise? G-d would have taken him to Jerusalem, the Jerusalem of High, which has not yet been revealed to us. Paradise is a place I know from before; Jerusalem above, I have never experienced. Now, I must be satisfied with Paradise on Shabbos; in the future we hope to be brought to Jerusalem of High.from The Soul of Shabbos.
I have always thought that the idea of an 'extra soul' received by all Jews on Shabbat is a beautiful idea. At the same time, I wasn't really sure what to do with it--that is, until recently. After Shabbat I will post some more thoughts on this subject. Until then, perhaps thinking over this idea will lead you to insights of your own! If so, please share them!