The gemara tried to say a gezeras shavah to explain why terumas shekalim starts in Nissan,from the past of "Rishon Hu l'Chodshei ha'Shanah".
But how can we use that pasuk, when just previously, we tried to use this pasuk to learn that it is the "Rosh Ha'Shanah l'Chodoshim" and we failed to definitively prove that it is even reffering to the month of Nissan, it could have been Adar or Iyur that the pesukim were reffering to ...
Isaac Lubin, United States
Dear Isaac,
In the end, Nissan is for sure the first of months, as the Braisa says and therefore the Gemara bases that Shekalim is in Nissan on what it knows definitely (even if it was difficult to prove) that Nissan is the first of months. That is what Rishon Hu really means- and after that the Gemara connects Shekalim to it.
Aall the best,
Reuven Weiner