Sacrifices must be brought only in the Temple. The thirteenth perek (=chapter) of Masechet Zevahim, which began on yesterday’s daf (=page) focuses on the prohibition against bringing sacrifices outside of the Temple. This prohibition is not connected with idol worship, for even sacrifices whose intent is to serve God can only be brought in the Temple. Slaughtering or sacrificing an animal outside of the Temple is considered to be a very severe violation of Torah law (see Vayikra 17:3-9), and carries with it the punishment of karet – “excision” – which is generally understood to mean premature death.
This requirement, which was in effect in the desert when sacrifices were brought in the Tabernacle, was implemented again when the Solomon built the Temple in Jerusalem. In the interim, under certain circumstances, korbanot were permitted on bamot – “high places” – which were altars on which sacrifices were brought.
In our day, when the Temple is no longer standing, what is the status of someone who brings a sacrifice? Rabbi Yohananrules that it is forbidden and he is held liable; Resh Lakish rules that he is not held liable. The Gemara explains that their disagreement is based on the question of whether the original sanctity of Israel still remains. If the sanctity of Jerusalem remains, then sacrifices can only be brought on the Temple Mount, even if the Temple is not standing. If the sanctity no longer exists, then we revert to the situation where sacrifices would be permitted to be brought anywhere.
The simple reading of the Gemara appears to view the holiness of the Land of Israel and that of the city of Jerusalem as being the same, so if the destruction of the Temple removes the holiness from the Land, it does so for Jerusalem as well. This, in fact is the approach that is taken by Tosafot. The Rambam, on the other hand, sees the two as distinct and rules that even if the holiness of the Land is removed, kedushat Yerushalayim – which stems from the presence of God – can never be removed. With the return of the Jews to Israel under Ezra ha-Sofer and the building of the second Temple, the center of the kedushah was the rebuilt Temple – the seat of the Almighty – and the rest of the Land derived its holiness from Jerusalem. Thus the Rambam rules that even with the destruction of the Temple, kedushat Ezra remains forever.