Detached Or Unrelated
‘He Made An Asheirah Tree Into a Ladder…’
The Gemara asks whether branches of a tree growing along a wall can serve as a natural ladder to create a pesach – a portal – enabling two separate courtyards that abut the wall to join in an eruv. If they can, the Gemara asks further whether they still can if these branches belong to an asheirah tree (which were worshipped by idolaters).
The Invisible Lion
R. Chisda maintains that an asheirah tree can serve as a pesach even though the Torah (Devarim 7:5, 12:3) forbids deriving benefit from it (which means that it is biblically prohibited to use it as a ladder to scale a wall). R. Chisda likens this asheirah pesach to a lion crouched near a doorway preventing passage through the door. He reasons that even though it is forbidden to use the asheirah pesach, it is a pesach nonetheless, just like a doorway with a lion standing in it is considered a pesach despite the danger (impossibility?) of using the doorway.
R. Chisda limits his reasoning to prohibitions (like benefiting from an asheirah tree) that are unrelated to Shabbos. However, if a Shabbos-related issur prevents passage through the doorway or over the wall, then the courtyards cannot join in an eruv. Therefore, R. Chisda says that an ordinary tree cannot serve as a pesach because climbing trees is a Shabbos-related issur. One may not climb trees (Eruvin 100a) lest one forget and break off a branch and violate the melachah of plowing or reaping (Shabbos 107b, 108a based on Shemos 34:21).
The Ritva (ad loc.) points out that climbing an asheirah tree on Shabbos involves two issurim: a) the issur of benefiting from avodah zarah and b) the rabbinic ban against climbing trees on Shabbos. Hence, the Ritva asks why R. Chisda ignores the Shabbos-related issur of climbing trees when validating a pesach created by an asheirah tree.
The Ritva answers that the Gemara is referring to an asheirah tree that is detached from the ground, and the issur of climbing trees does not apply to a detached tree (because if one were to break off a branch from a detached tree one would not violate the melachah of kotzer).
It Transcends Shabbos
Alternatively, Rabbi Akiva Eger argues that the rabbinic issur to climb trees on Shabbos does not apply to an asheirah tree (even when it is attached to the ground). He explains that we are not concerned that someone will accidentally break off a branch from such a tree on Shabbos since he knows that the Torah forbids him from deriving benefit from asheirah trees (even during the week) due to the issur of avodah zarah. Therefore, the only issur involved in climbing an asheirah tree on Shabbos is benefiting from avodah zarah, which is not a Shabbos-related issur.