Dear Rabbi Kornfeld,
Why is the kinyan chatzer of a get on Shabbos less problematic than just giving it? Both are assur on Shabbos mishum mekach umemkar?
Gershon
We understood it as follows: Rava could not simply permit the Shechiv Mera to pick up the Get and give it to his wife on Shabbos, because a Get is Muktzah on Shabbos and it is Asur to handle Muktzah. In contrast, making a Kinyan on Shabbos -- although the Rabanan prohibited it under normal circumstances, they never prohibited it in the case of a Shechiv Mera. Hence, it is permitted to begin with for a Shechiv Mera to make a Kinyan in such a situation, but to handle Muktzah would be a transgression of the Isur d'Rabanan of Muktzah. See also TOSFOS (DH v'Teizil) who seems to learn this way.
Y. Shaw
If I understand it correctly, Tos. is quoting Rashi here, and this is also brought in the Rosh and the Ran. See also the Korban N'sane-l on the Rosh who says that the problem with Tiltul is that it does not accomplish the Geirushin [immediately, but rather the person is Over the Isur of Tiltul Muktzah and only afterwards does the Gerushin take effect, while, in contrast, when he is Makneh the land to her, the Gerushin takes effect simultaneously with the Hakna'ah].
Kol Tuv,
Yitzchok Zirkind