Sukkah Intentions

The Tur (Orah Hayim, 625; and later the Shulhan Arukh, ad loc.) introduces the laws of living in a sukkah by saying that the mitzvah is so that we remember that God had us live in sukkos in the desert after the exodus from Egypt. R. Yoel Sirkes, the Bah, asks why the Tur mentions this theological idea in his practical compendium. He answers that this idea has a practical application. The Torah tells us that we must live in a sukkah "in order that future generations may know that I made the Israelite people live in booths when I brought them out of the land of Egypt" (Lev. 23:43). Therefore, writes the Bah, when one sits in a sukkah one must consciously remember the historical origin of the sukkah in order to fulfill the commandment.

This innovation of the Bah is accepted by all major posekim, with the only debate centering around the case of someone who failed to remember this historical origin. Has this person ex post facto (be-di-avad) fulfilled the commandment or must he repeat it? Many (e.g. Bah, Bikkurei Ya'akov, Derekh Pekudekha) hold that he has not fulfilled the commandment while others (e.g. Peri Megadim, Mishnah Berurah) hold that he has and need not repeat the mitzvah act.

What leaves me dumbfounded is not the details of this matter but its methodology. Without any mention in the Talmud or medieval literature, this innovation was accepted unanimously. The Bah essentially created his own exegesis of a biblical verse in order to create an obligation (granted, in order to solve a textual problem in the Tur).

I am not the first to notice this anomaly. R. Moshe Shternbuch (Mo'adim U-Zemanim, vol. 1 no. 85) also expressed surprise at this innovation... and therefore concluded that this can only be an ab initio (lekhatehilah) obligation but not ex post facto.

I simply fail to understand how this methodology of post-talmudic biblical hermeneutics can be used. However, since the posekim have unanimously accepted this innovation, no one has the right to ignore it and I certainly defer to their authority and expertise.