1) Although guarding is allowed on Shabbat, the Sages created this prohibition against receiving wages, so that people wouldn't come to do business on Shabbat itself (and come to write something down, which is a biblical prohibition). The case here is that one agreed to pay the guard a daily rate, and thus, due to this prohibition, one doesn't have to pay him for the guarding he chose to do on Shabbat; consequently, the guard is not responsible for any damage to the property which occurs on Shabbat. Even if the employer wants to pay, the guard isn't allowed to accept it, unless it was given in the form of a gift (See Shulchan Aruch 306:4 and the Mishna Berurah there). 2) Then the guard is responsible for any damage that occurs to the object on Shabbat.

1) The Sages forbade any sort of transaction on Shabbat, out of concern that people may come to write something down, which is a biblical prohibition. Giving a gift is included in this prohibition, because it entails a transfer of ownership. 2) Or for the purpose of performing a mitzvah (Beit Yosef 527). It's preferable not to give a Bar Mitzvah or wedding present on Shabbat (Magen Avraham 306:15), however, Rabbi Akiva Eiger permits sending a gift to a groom. If one does receive a gift on Shabbat, one should have intention not to acquire it legally until after Shabbat. Some authorities permit giving a gift to a Gentile on Shabbat.

1) Some say this prohibition was enacted out of concern that one may erase part of the contents, thereby violating a biblical prohibition; others claim that this falls under the general prohibition of ''pursuing your affairs'' which this chapter deals with. (Mishna Berurah 307:51). 2) See Laws 2 and 6 above. 3) See Law 2 above. 4) Things which are forbidden to read on Shabbat, are ''muktzeh''. (Taz 307:17).