Exode 31:17

between My Word and the sons of Israel it is a sign for ever. For in six days the Lord created and perfected the heavens and the earth; and in the seventh day He rested and refreshed.

וביום השביעי שבת, seeing that on that day the creative activity of G’d had been completed, completion spells rest,

וינפש, this is why the seventh day is one devoted to the נפש, the spirit, resulting in G’d giving Jews an additional soul for use on that day. This additional soul assists us in concentrating on the spiritual dimension of the day. When man was created, G’d made him in His image, i.e. first and foremost concerned with spiritual concerns. The extra soul granted us on the Sabbath is to help us live up to that vision G’d had of man when He created him. (compare Beytzah 16)

וביום השביעי שבת וינפש, “but on the seventh day He rested and withdrew into His essence.” Rabbi Yehudah Hachassid said that from this verse we can deduce that the Jew receives an additional soul on the Sabbath. When you read the respective last letters in the last four words of the verse backwards, you get the word שתים, “two.” The Talmud relates an interesting conversation between Rabbi Akiva and Turnusrufus, the wicked Roman governor during part of his life when the latter met him once on the Sabbath. Upon seeing him, the governor asked Rabbi Akiva what was so special on that particular day, to which Rabbi Akiva replied: “how are you different from anyone else?” Turnusrufus wanted to know what kind of an answer this was to his question. The Lord had singled him out to be more honoured than other human beings. Rabbi Akiva told him that the same Lord had singled out the Sabbath to be more honoured than any other day He had created. Turnusrufus then wanted to know why that same G–d performs all manner of work on the Sabbath, such as letting the wind blow, the rain fall, etc., whereas He denied the Jews to work on the Sabbath and to travel on the Sabbath? Rabbi Akiva replied that he was aware that the governor was familiar with the Torah G–d had given the Jews, so that he could ask him, why if two Jews share the same courtyard in front of their houses, what is the reason for the law whereby if each of the homeowners does not enter into an arrangement whereby he foregoes his legal claim to the courtyard, neither of them can move his chattels in that courtyard on the Sabbath, whereas when they each waive their claim, they can both use that courtyard freely? How come, he continued, that if a Jew has a palace owned exclusively by himself, and surrounded by a courtyard as large as the city of Damascus, he is free to move all his chattels all over that courtyard on the Sabbath? Similarly, the Lord Who owns both heaven and earth exclusively, is free to let the wind blow and to let the rain fall without thereby violating the laws of His Sabbath. He added, that if proof were needed for what he had told the Roman governor, let him reflect on the fact that that same Creator observed the Sabbath by not having given the Jews in the desert their heavenly bread, manna on that day, but giving them a double portion on the Sabbath eve, so that they would not go hungry on that day. (Tanchuma, section 33 on this portion)