The gemara (Pesachim 25b) discusses a case of walking through a market and getting hana’ah from the scent of avodah zarah perfume – the issue depends on a combination of considerations as to whether it is possible to take some other path and whether or not one has kavanah to get benefit from the fragrance (2 leshonos in the gemara as to the details of a machlokes Abaye and Rava). The gemara relates this issue to the classic machlokes R’ Shimon and R’ Yehudah by davar she’eino mitkavein - if I drag a chair across my lawn on Shabbos, the fact that a furrow gets plowed does not make me chayav because my intent defines my action as dragging a chair, not an act of plowing (according to R’ Shimon). Apparently the same underlying consideration operates in the fragrance case as well – intent helps define whether one engaged in the act of simply walking through the marketplace or an act of deriving hana’ah from avodah zarah fragrance.
With this background, we can explain the Rashba and Ba’al haMaor (see postings earlier this week). We asked: if mitzvot lav le’henot nitnu (mllh”n) is a meaure of a shiur of hana’ah and the hana’ah of having been yotzei a mitzvah does not meet the threshold of significance to be prohibited, nonetheless, if there is a physical hana’ah associated with the mitzvah act it should meet the shiur of hana’ah and cause the act to be assur – how can the Rashba disagree? R' Soloveitchik suggested (see also Shiurei R' Shimon Shkop, Nedarim) the Rashba may hold that violating an issur hana'ah requires an ACT of deriving hana’ah from the issur. Mllh"n is not a measure of the quantity of hana'ah, but a definition of the act one is engaged in as not being a ma'aseh issur. Just as in the case in Pesachim the consideration of kavanah causes us to view one's action as simply walking through the marketplace and not an act of being ne’hene from issurei hana’ah, the fact that one is engaged in a ma’aseh mitzvah causes us to define one's action as a ma’aseh mitzvah and not as an act of hana’ah even if there is a physical hana'ah that goes hand in hand with the same action. With this sevara one can understand the distinction between issurei d’oraysa and issurei derabbanan. By issurei d’oraysa, the command of the Torah defines the specific act as a ma’aseh mitzvah and not an act of hana’ah. However, by a kiyum derabbanan, the specific act is question was never commanded by the Torah, and so we are forced to consider the personal hana’ah involved. Returning to the Ba’al haMaor, the distinction between shofar and chatotzros cannot be between mitzvot d’oraysa and mitzvoth derabbanan (as some understood), because blowing chatzotzrot is itself also a mitzvah d’oraysa. However, one can distinguish between the two different mitzvot of blowing (as noted in the comments previously). By tekiyas shofar, the mitzvah is incumbent on each individual, and so each individual’s blowing is defined as a ma’aseh mitzvah and not a ma’aseh of hana’ah. However, R’ Soloveitchik suggested (Mesorah journal, vol 5) that the mitzvah of blowing chatzotzros is a chovas hatzibur, a communal obligation, and so we cannot point to the act of any one individual and say that is a ma’aseh mitzvah commanded by the Torah and not a personal act of hana’ah.