Eiruvin 40a, b

The focus of today's daf reminds me of Masechet Brachot.  The rabbis debate further about 2-day Festivals and about Rosh HaShana, a 2-day Holy Day. Beginning with the question of whether or not an animal slaughtered by a gentile and intended for one Jew might be permitted to other Jews on the second day of a Festival (as an aside, another interesting tale involving the power of an exilarch and the special status of Torah scholars is shared in 40a).

The rabbis go on to debate about particular prayers and how they might be redundant or permitted on the second day of a Festival, on a Shabbat and Rosh Chodesh, or on other coinciding holidays.  

I have wondered about the halacha of related questions in the past.  How would we light candles for the second night of a festival? Why would we say shechechayanu (or as they name it in Eiruvin 40, the time prayer) on the second night of a chag?  In fact, why would we not say shechechayanu much more often; at any time-bound opportunity?  I have learned most of the halachically based answers to these questions, but I have not had the opportunity to appreciate the thinking behind those laws.

One of the things that I love most about my reading of Talmud is the seemingly arbitrary reasoning used by the rabbis in establishing our rituals and traditions.  They turn to sources, but those references often seem vague to me.  I can come up with sources, too, and so can anyone - particularly those who are steeped in Torah.  So why are the particular reasonings of the rabbis taken as unquestionable law?  Regardless of why it happened, it happened, and these words that I am reading about the very process of creating law are foundational.  Simply incredible, humbling, and inspiring.  But not halachically inspiring - to me.