Re'eh 5777

As Moshe continues to lecture to the nation, he mentions not to add or subtract from the commandments (13:1). Rashi quotes a Sifri that says we are not to add a fifth section in our tefillin, a fifth type of plant with the lulav bundle, or a fourth blessing in Birkat Kohanim. Both the Maharal and Maskil Le'David ask the following questions: Moshe had already warned the nation of adding or subtracting back in Parshat Va'etchanan (4:2), why is he repeating himself? Secondly, Rashi over there quotes the same teaching of the Sifri with one change where he says not to add a fifth tzitzis; why does he change it to Birkat Kohanim?
Both commentaries give a single answer that addresses these questions. With tefillin, lulav, and tzitzis, the person is intending to add on to the essential fulfillment of the commandment; they want to add an extra part to the action. That, says the Torah in Va'etchanan, is the primary prohibition of adding or subtracting. But what about adding onto the commandment once one has fulfilled the obligation? This is why Moshe repeats the prohibition again and Rashi adds Birkat Kohanim. When the Kohen recites the third blessing, he has fulfilled his obligation of blessing the people. However, he is not allowed to add a fourth blessing on his own accord even if he has done the full action already.
The Torah is teaching us that it is important to never overdo things. There are set limits and regulations in order to maintain order in the world. Once we begin to be flexible with rules we begin to alter fundamental beliefs and values we have.