Pesachim 26a, b

Today is Tisha B'Av.  Traditionally we remember the destruction of the first and second Temples in Jerusalem.  Coincidentally, daf 26a focuses on Temple practices as examples of when we are allowed to 'derive benefit' from something that is ordinarily prohibited.  This is a continuation of the rabbis' attempts to understand when and where and why we might be allowed to benefit from chametz during (or close to the start of) Pesach, when chametz is otherwise prohibited.

Some of these examples include using the shade of the Temple to conduct lectures on mitzvot, smelling the sanctified incense prepared only for the Temple, how to use the ashes and the priestly garments left behind at the Temple, and how to use the heifer whose neck is broken or the red heifer (both of which are designated only for a specific purpose and specifically not for other purposes).  Each of these examples is discussed at some length.

As an aside, a principle is defined in daf a.  When two statements regarding exclusion are written in the same sentence, we do not generalize that halacha.  Instead, we apply the halacha only to those statements.  Words like "it" and "the" as in "the red heifer" help us to know that we are learning only about that one red heifer and not about heifers or birds or even red heifers in general.

Daf b introduces a number of new examples regarding how we might derive benefit from an item otherwise prohibited.  One example is the use of a found blanket being used to keep guests warm.  Another is selling or even carrying garments made of 'diverse kinds' (the fabric of two different crops, for example wool and linen, are not to be sewn together) (Deuteronomy 22:11).  And yet another example still current today is whether and how an oven may be used after it has been heated or strengthened by a prohibited item.  

While our circumstances are generally very different from those of our Sages, these conversations are not.  Many streams of Jewish tradition continue to value learning, searching, discussing and interpreting.  As we mourn the loss of our Temples, we can be grateful for the continued opportunities to debate our traditions and interpretations of those traditions.