552. Brachos on Rabbinic Mitzvos

Brachos 11:3

When it comes to all Rabbinic mitzvos, a bracha is recited before both those that the Sages instituted as obligations - such as reading the megillah, lighting Shabbos candles and lighting the Chanukah menorah - and those that are not obligations – such as making an eiruv or washing hands before eating (which is voluntary in that one need not necessarily eat bread). In either case, one recites a bracha that God “has sanctified us with His commandments and commanded us (to perform such-and-such mitzvah).” And where, precisely, did God command us to perform Rabbinic mitzvos? Deuteronomy 17:11 says, “Act as they shall direct you.” This means that God sanctified us with His commandments and commanded us to listen to the Sages, who commanded us to light the Chanukah menorah, read the megillah, etc.

Brachos 11:4

Why do we not recite a bracha before mayim achronim (washing our hands after a meal)? Because the Sages only instituted this because of a potential danger. Brachos are not recited over something done to obviate a potential danger. It’s like one who strains his water at night because of the possibility of leeches. Such a person would not recite a bracha that God commanded us to strain water. This principle is true in all such cases.