In his work on the laws of shabas called Kalkalas Shabas (at the beginning of the 3rd chapter), the author of Tif'eres Yisra'el introduces the topic of muktzeh by saying that the reason the sages prohibited use of non-essential objects on shabas was
כדי שיהא שביתת האדם ניכרת שהיא כמצות התורה למען ינוח, שיהא לבו פנוי לתורת ה' ביום שבת.
so that a person's cessation would be recognizable as the Biblical commandment "so that one shall rest", such that his mind could be available for God's Tora on shabas day.
From the way he phrases the next few lines, his contention seems to be not just that this is a reason for the prohibition against moving muktzeh objects, but the primary reason therefor.
As opposed to the opinions of Ramba"m and Ra'ava"d, quoted further in the paragraph, which hold that muktzeh laws were instituted to prevent forbidden activities being done with the objects in question, the Tif'eres Yisra'el appears to believe they were meant to simply free up a person from quotidian busywork, which would detract from his learning/spirituality (or to represent such a freeing up).
Is there an earlier source for this explanation of the laws of muktzeh - stated as a primary reason or otherwise? It seems pretty extreme and is unsourced, unlike the other explanations he includes.