The opening verses of Parashat Ki-Tisa introduce the mitzva of machatzit ha-shekel – the half-shekel tax imposed upon every member of the nation. As the Ramban discusses at length in his opening comments to this parasha, the Sages understood these verses as referring to three distinct commands. First, the Torah here requires that when a census is conducted, the people must be counted by way of half-shekel donations given by each member of the nation. Implicit in this command, the Ramban writes, was the second requirement – to count Benei Yisrael at the time this command was given, at the time of the construction of the Mishkan. And thus in the beginning of Parashat Pekudei (38:25-28) we read that the people had donated silver half-shekels for the census, and this silver was used (mainly) for the sockets that formed the foundation of the Mishkan. The third obligation is the annual half-shekel tax that was collected to fund the public sacrifices and maintenance of the Beit Ha-mikdash.
While the consensus view appears to be that all these three requirements are included in the machatzit ha-shekel command presented in these verses, a unique position is taken by the Vilna Gaon, in Aderet Eliyahu. The Gaon’s approach is unique in two respects – in his understanding of the Torah’s command vis-à-vis the census, and in his understanding of the annual half-shekel tax.
According to the Vilna Gaon, the law concerning the census is presented only in the first verse (after the introductory verse, “The Lord spoke to Moshe”), which states that when the nation is counted, everyone must give “kofer nafsho” (“a ransom for his soul”). This verse makes no mention whatsoever of the amount of a half-shekel, and the Gaon explains that this amount was not required when taking a census. As the Gaon observed, King Shaul used other means of counting when conducting a census (Shemuel I 11:8, 15:4). In the Gaon’s view, some means of “atonement” is required when taking a census, but not specifically a half-shekel. This is in contrast to the conventional understanding, that specifically a half-shekel is required when taking a census.
The amount of a half-shekel is mentioned here in Parashat Ki-Tisa only in the next verse, and according to Gaon, the rest of this brief section refers entirely to the mandatory donation of silver towards the construction of the Mishkan. Beyond the first verse – which speaks of the need for some sort of “atonement” when conducting a census – the Torah here speaks only of the one-time tax needed to supply the silver that formed the foundation of the Mishkan. The Torah does not, in the Gaon’s view, speak here at all of the annual half-shekel tax that was collected for funding the operations of the Beit Ha-mikdash. This requirement, he contends, was taught via oral tradition (“halakha le-Moshe mi-Sinai”), and is not actually stated in the Torah.
The Gaon answered on this basis the question raised already by the Ramban, in his Torah commentary (30:15), regarding the Torah’s command forbidding donations of more or less than a half-shekel: “The wealthy one shall not add onto, and the impoverished one shall not diminish from, the half-shekel [amount]…” The Ramban noted that the Torah here appears to impose a strict prohibition against paying a higher or lesser amount for the machatzit ha-shekel obligation, and yet, the Rishonim who listed the Torah’s commands did not include this prohibition in their list. According to the Gaon’s approach to these verses, of course, this is no question at all. Since these verses refer only to the one-time half-shekel donation required at Sinai, they do not establish eternal Torah law such that this prohibition should be counted among the 613 Biblical commands.
As mentioned, the Gaon’s view does not represent the standard understanding. Thus, for example, the Rambam in Sefer Ha-mitzvot (asei 171) and in the opening passage of Hilkhot Shekalim writes explicitly that the annual half-shekel tax constitutes a Biblical command, introduced here at the beginning of Parashat Ki-Tisa.