Did Allah designate Saturday for the Jews and Christians to rest? Or do they rest because they believe Allah rested after creating the earth?
No, this day was not designated for them. In fact Friday was designated for them but they changed it.
“Narrated Abu Huraira (رضى الله عنه): I heard Allah's Apostle (ﷺ) saying, "We (Muslims) are the last (to come) but (will be) the foremost on the Day of Resurrection though the former nations were given the Holy Scriptures before us. And this was their day (Friday) the celebration of which was made compulsory for them but they differed about it. So Allah gave us the guidance for it (Friday) and all the other people are behind us in this respect: the Jews' (holy day is) tomorrow (i.e., Saturday) and the Christians' (is) the day after tomorrow (i.e., Sunday)."
Possible their belief was also misguided by believing they are resting because Allah rested.
 [Saheeh Al Bukhari: Volume 2, Book 13, Number 1]< Back to Questions