The 16 expressions of forgiveness

Black like a raven or a beauty?

Regarding the commandments of the Torah it states: "don't me more righteous than your creator, to forbid things that are permitted to you.״ 

The forbidden object itself is repulsed, even though there is certainly a divine spark within it. The pushing away of these things from holiness is compared to the cruelty of the raven, שחורות כעורב - "dark like the raven."

However, the decrees of our sages go one step further, to forbid that which is permissible, such as birds meat with milk or the fat of the gid hanasheh. For this reason the words of our sages are called דברי סופרים - words of the scribes, higher than ספר, than the book itself. On this it's written, in comparison to the blackness of the raven above, שחורה אני ונאוה, I am black and beautiful.

This is similar to how the negative commandments are higher than the positive commandments, in their exalted, aloof nature.

This is also the level of Nedarim, to forbid for yourself that which is permissible. Thus you can make a neder to usurp a mitzvah (such as not to drink wine, contravening kiddush).

Ohr Hatorah Matos