As we said in the previous mitzvah, the word “elohim” can have multiple meanings. Here, it is taken to mean God.
One might ask why this injunction counts as two distinct mitzvos. The Rambam, in the last of his 14 principles for identifying the 613 mitzvos, tells us that if the Torah tells us the penalty for an action, the prohibition must also be found somewhere. Since we see the penalty for blasphemy (Leviticus 24:16), we have to see where it’s prohibited. The Rambam tells us that it’s here: the same verse prohibits cursing both judges and God. (See also the discussion of a “lav she’bichlalos” in his ninth principle.)
The idea of cursing God is so reprehensible that we don’t even call it that in Hebrew. In Hebrew, it’s called “birkas Hashem,” which means “blessing the Name (of God).” It’s a necessary euphemism because the idea of cursing God is so utterly unthinkable (or should be!).
The reason for the mitzvah is clear: God is the source of all. Everything He has given us is for our good. To curse Him (God forbid!) is to spurn all He has done for us. It is especially a misuse of the power of speech, which He has given exclusively to mankind. Blasphemy is so reviled that, upon hearing it, a Jew is to rip his clothes as he does in mourning. (In II Kings 18, the servants of the king tore their garments upon hearing blasphemy from Ravshakeh, an apostate Jew.)
This mitzvah applies to both men and women, in all times and places. It is discussed in the Talmudic tractate of Sanhedrin on page 56a. In the Mishneh Torah, it is found in Hilchos Avodas Kochavim chapter 2. It is #60 of the 365 negative mitzvos in the Rambam’s Sefer HaMitzvos. Even though this mitzvah is in effect today, the Chofetz Chaim incorporates it in his treatment of the previous mitzvah in his Sefer HaMitzvos HaKatzar.