Negative Commandments #159 & 160
Sefer Ha’mitzvos Ha’Katzar (The concise book of mitzvos)
By the Chofetz Chaim
This book lists the Torah mitzvos that can be observed today
Second Section – the Negative Commandments
159. It is a negative commandment "do not add a commandment to the Torah."
As it states in Devarim (Deuteronomy) 13:1, "do not add on it."
160. It is a negative commandment "do not take away a commandment from the Torah"
As it states in Devarim (Deuteronomy) 13:1, "do not subtract from it."
This applies to commandments from the Written Torah and commandments from the Oral Torah. If a person states that a commandment from the Sages is a commandment from the Torah, this is a transgression of adding. If he takes away a commandment from the Torah, it is a transgression of subtracting. But, our Sages of blessed memory were allowed to add Rabbinic commandments which were added as fences or edicts or, for example, the reading of the Megillah or lighting Chanuka candles, because these were praise and thanksgiving to G-d. These Rabbinic commandments are not against the commandment of not adding because the Sages did not state that these were G-d commanding us a new commandment to add it to a commandment from the Torah.
If a Cohain adds one blessing in the three blessings of the Cohain's Blessing that is written in the Torah, this is adding and transgresses this commandment.
This applies in all places and at all times, for men and for women.