Did you ever wonder why on Shabbat you go to Shul later than on weekdays? When instructions were given concerning the daily sacrifice the Torah says: אֶת הַכֶּבֶשׂ אֶחָד תַּעֲשֶׂה בַבֹּקֶר, “The one lamb you shall make in the morning…”. (Num. 28,4) When instructions are given for the Shabbat sacrifices the Torah says: וּבְיוֹם הַשַּׁבָּת שְׁנֵי כְבָשִׂים, “And on the Sabbath day two male lambs…”. (Num. 28,9) No mention is made of morning. It was thus permitted to bring later in the day. Hence the Shabbat services may start later and one has an opportunity to sleep later. This trivia is brought by no one less than the Rama in the Shulchan Aruch. (OC 281)
This is part of our Oneg Shabbat. It does not mean that you can sleep the entire Shabbat and do nothing. Shabbat is a time of rest but it is also a time to study and to improve your religious knowledge. It is a time to spend the day in a religious experience, something that is limited during the weekdays when we are preoccupied with our daily responsibilities.
The Shabbat should be spent by elevating our spiritual lives and increasing our knowledge of our Jewish existence.