Shavuos: Yetziv Pisgam Theory

Yetziv Pisgam is a piyyut in praise of Yonasan ben Uzziel, who wrote the targum on the books of Nevi'im [prophets]. Outside of Israel, where two days of Shavuos are celebrated, Yetziv Pisgam is sung in many congregations during the haftarah reading on the second day of Shavuos, after the first verse of the haftarah is read. The reason it is recited at this specific point in the service is that it introduces and praises the meturgaman [translator] who, in earlier times, would translate each pasuk of the haftarah into Aramaic after it was read in the original Hebrew.

A question can be asked: given that the practice of using a meturgaman took place each and every Shabbos, why was this piyyut in honor of the targum specifically composed for, and recited on, the second day of Shavuos?

A possible answer is based on the famous mishnah of Ain Dorshin (Chagiga 2:1) which indicates that certain very deep and inscrutable sections in the Torah/Tanach are not to be translated or taught in too open a matter. One of these is the “"ma'aseh merkava", the description of the heavenly chariot and image of God's glory, found in Chapter 1 of Ezekiel. Now, this very chapter is actually read as the haftarah on the first day of Shavuos. Thus, as per the restrictions of Ain Dorshin, the haftarah was not allowed to be translated on that day, so the meturgaman had the day off, so to speak. Therefore, at the start of the haftarah on the second day of Shavuos, we recite Yetziv Pisgam to re-introduce and praise the meturgaman, who was conspicuously absent the day before!