According to R' Ami, Rebbe instructed his students to arrange stones for sitting before shabbos. R' Ami appears to hold that wiping mud off of the stones would not suffice to designate the stones before shabbos, because such wiping is an "miniscule" act (Rashi, according to Maharsha). Only a more significant act of arranging the stones would suffice to properly designate them.

Yet in explaining our mishna, R' Ami holds that even if a rock is arranged (i.e., placed with intent) on top of a barrel as a lid before shabbos, the rock may not be removed on shabbos (nor may the barrel be lifted). Here, R' Ami appears to hold that a rock retains its muktza status despite being "arranged."

How does one reconcile R' Ami's understanding of the story of Rebbe with R' Ami's understanding of our mishna? Particularly, how does one distinguish the relative insignificance of placing a rock on top of a barrel as a lid from the significance of arranging a rock for sitting? (Even if a rock is not generally used as a lid for a barrel, shouldn't the act of consciously placing the rock on top of the barrel suffice to make it a into a lid?)

On a related note, why, according to Rashi, is Rebbe concerned with his students "touching" the stones on shabbos? Shouldn't Rebbe's concern be over moving the stones? I think the Shulchan Aruch expresses a similar concern in stating that the rocks cannot be "sat on" without proper designation from before shabbos.

Thank you,

David Kohn, Springfield, NJ