Muktze (lit. “set aside”) are items which our Sages forbade to move on Shabbat and accordingly, the prohibitions associated with Muktze are, generally speaking, Rabbinic in origin. The Gemara (Shabbat 124b) explains that these laws were instituted to prevent one from taking out objects into the public domain where an Eruv does not exist.
The Rambam (Shabbat 24:12) also offers several reasons as to why our Sages instituted the concept of Muktze. The first reason is to create a safeguard against the possibility of using forbidden objects on Shabbat. If one is forbidden from moving a certain object then it reduces the chance of one actually using said object. Another reason is to create a greater distinction between weekdays and Shabbat, especially for people who do not work during the week. If one is not occupied with laborious activities throughout the week and would normally be able to handle certain items on Shabbat, there would be very little difference in that person’s experience of a weekday versus Shabbat. Furthermore, if one is able to handle these objects, then there is a concern that one will be spending all one’s time on Shabbat moving them around, which compromises the very notion of how one is supposed to spend one’s time on Shabbat.
In all Rabbinic enactments, such as Muktze, there are reasons as to why our Sages decided to institute them. Additionally, the Gemara (Pesahim 30b) says that our Sages were inspired by the Torah law when instituting these enactments. As such, Rabbi Elhanan Wasserman (hy’d) writes (Kovetz Shiurim Beitzah 3b) that the Sages’ inspiration from the Torah for Muktze was from the Biblical prohibition of carrying in a public domain, but that the reasons for this enactment are those offered by the Rambam.
There are two broad classes of Muktze, the first being items which have a Halachic status of a Kli, or a vessel, and those which do not have that status. Although Kelim typically are allowed to be moved on Shabbat, there are certain types of objects that are considered Muktze and it is this class that will be discussed presently.
Summary: Muktze refers to objects which our Sages forbade from moving on Shabbat.