The Sages prohibited moving things that are not fitting for Shabbat and that one puts out of his mind (maktzeh mi-da’ato). There are two fundamental reasons for this prohibition: 1) to preserve the atmosphere of Shabbat as a day of holiness and rest. The idea of rest applies to one’s hands as well; they should not move objects or be involved with activities that are not connected to Shabbat; 2) to set up a safeguard so that one will not come to do melakha on Shabbat. We will begin by explaining the first reason.
In addition to the melakhot that are prohibited on Shabbat, the Torah commands us to rest and relax on Shabbat, as it states: “but on the seventh day you shall cease, so that your ox and your donkey may rest, and the son of your maidservant and the stranger may be refreshed” (Shemot 23:12). Similarly, we read: “Six days shall work be done, but on the seventh day there shall be a Shabbat of complete rest, holy to the Lord” (Shemot 31:15). In order to fulfill the Torah commandment to rest and relax on Shabbat, the Sages established several ordinances meant to protect the spirit of Shabbat as a day of sanctity and rest. One of them is the prohibition of muktzeh.
If moving items unnecessary for Shabbat were permitted, people might well spend all of Shabbat cleaning and arranging their homes and belongings, thus negating the mitzva to rest. Additionally, the prophets instructed the people that the atmosphere of Shabbat should be different from that of the weekday – one should walk and talk differently. Following this line of thought, the Sages decreed that people should not handle objects and implements on Shabbat in the same way as during the week. This way Shabbat is truly felt by all, including those whose weekday activities do not normally involve any forbidden melakhot. We see that the prohibition of muktzeh is rooted in the words of the Torah and the prophets, while its precise parameters and details are rabbinic (AHS 308:4-5; above, 22:1).
As we said, the second reason is so that one will not end up doing melakha on Shabbat. As with all mitzvot, the Sages instituted safeguards in order to distance people from sin. The prohibition of muktzeh makes it less likely that people will carry objects in the public domain or use muktzeh items to perform melakha (Rambam and Raavad, MT 24:12-13).
The prohibition of muktzeh synchronizes the mind and the hands. Any item that one knows is not fit for use on Shabbat will not be touched by his hands either.