Responsum of HaRav Yisrael Ariel
Question: ... I would appreciate your replying to my question can the commandment of Mahatzit Ha-Shekel be fulfilled with Torah validity at the present time?
Response: It is widely known that after the destruction of the First Temple the Jews returning from Babylonia, upon reaching the country, rebuilt the altar and offered sacrifices up on it for twenty two years, before the Temple was rebuilt. The question arises: how did the Babylonian returnees contribute the Mahatzit Ha-Shekel and how did they bring sacrifices for the altar, for the Second Temple had not yet been rebuilt, and the commandment of sh'kalim can only be fulfilled in the presence of the Temple (Shekalim 8:8)?
However, halakha rules, without dispute, that sacrifices are offered up even when the Temple itself is in ruins, as Rabbi Yehoshua is quoted in Tractate Eduyot (8:6) "I heard that [sacrifices] are offered up though there is no Temple", and as Maimonides adduces in his Hilkhot Beit Ha-Behira (2:4 and also 6:15). In light of this halakha, it can be understood why Second Temple officials collected Mahatzit Ha-Shekel from the returnees as they arrived, rebuilt an altar and offered sacrifices up on it, for the offering up of sacrifices is not conditional upon the Temple itself being rebuilt.
Regarding the Mishna which states that the commandment of Mahatzit Ha-Shekel applies "in the presence of the Temple", the Mishna is indicating a period of time, i.e., the commandment of Mahatzit Ha-Shekel applies only "in the Temple period", i.e., when preparations are being made to rebuild the Temple, Mahatzit Ha-Shekel is collected, though the Temple itself is as yet in ruins, while, at the same time, initial steps are taken for the rebuilding of the altar, for the offering-up of sacrifices and for the reconstruction of the Temple building. The obligation to donate Mahatzit Ha-Shekel even before the rebuilding of the Temple has begun derives from the Torah source of the commandment of Mahatzit Ha-Shekel: "This they shall give ... half a shekel [measured] in the holy shekel's and to give the money of atonement ... and you shall give it for the worship in the Ohel Mo’ed," i.e., the money is needed for the purposes of erecting the Sanctuary and its ritual. In other words, the commandment of Mahatzit Ha-Shekel is a preliminary step before the Sanctuary is erected.
The Talmud Yerushalmi states (Shekalim 1:1) regarding Mahatzit Ha-Shekel “Three contributions are mentioned in this context [in Teruma and in Ki Thissa] the contribution of the Sanctuary for the Sanctuary can be of any amount found suitable; the contribution of Shekalim for the sacrifices can be of any amount found suitable; and the contribution of the Foundations for the foundations: the rich may bring no more, and the poor no less”. The three contributions in the verse are the basis and the infrastructure for building the Sanctuary and for the offering-up of the sacrifices, without which there would be neither Sanctuary nor altar worship.
At any rate, even at the present time, the commandment of Mahatzit Ha-Shekel precedes the rebuilding of the Temple, and just as in the days of the Sanctuary and in the early days of the Second Temple Period, the commandment of Mahatzit Ha-Shekel served to initiate the construction of the Temple, so should it be with the building of the Third Temple may it be built speedily, in our days! the first step should be the fulfilling of the commandment of Mahatzit Ha-Shekel.
When the time comes, G-d willing, the appropriate agency will announce the collection of Mahatzit Ha-Shekel. The altar will be rebuilt on the Temple Mount and the kohanim will begin to offer up sacrifices. While the worship is in progress, the builders will complete the construction of the Temple upon its foundations just as the people of the Second Temple Era succeeded in doing.