(2006/5766) Most people appreciate it when a friend does something
extra for them, beyond what is required.  Strangely, the Torah
seems to contradict this concept!  It commands (4:2), “Lo
Tosifu Al HaDavar Asher Anochei Metzvaveh Etchem VeLo
Tigre’u Mimenu,” “Do not add on to the thing that I am
commanding you and do not detract from it.”  Why would
Hakodosh Baruch Hu not want us to add to the Mitzvot? 
Would that not further show our devotion to Him?
The Dubno Maggid answers with a Mashal:  There was
once a man who, whenever he borrowed an item from his
neighbor, would return the item with more of the same.  If he
borrowed a spoon, he would return two spoons; if he
borrowed bowls or platters, he would return twice as many as
he had borrowed.  One day, his neighbor asked the borrower,
“How come you always return two of what I lend to you?”  The
borrower answered seriously, “When I bring each item into my
house, it becomes pregnant and gives birth to another like it!” 
One day, the borrower asked his neighbor if he could borrow
his silver Menorah for Chanukah.  The neighbor gladly
handed him the Menorah, thinking to himself, “Tomorrow I’ll
get another Menorah!”  However, the Menorah was never
returned, even after several days.  When the neighbor asked                                                      the borrower what had happened, the latter answered, “I’m
very sorry, but when I brought the Menorah into my house, it
died.”  The neighbor, astonished, exclaimed, “But a Menorah
can’t just die!”  The borrower replied, “Well, spoons don’t just
give birth and have children either.  If you are going to
believe me about the spoon giving birth, you have to believe
my claim that the Menorah died.”
If we are Mosif – if we add to too much –we will
eventually come to be Gorei’a, to detract.
Based on this prohibition, the Rashba in his
commentary to Rosh Hashanah wonders how Chazal could
institute the blowing of extra Shofar blasts on Rosh
Hashanah.  After all, the minimal number of times, according
to the Torah, that one is required to blow the Shofar is only
nine; does blowing one hundred not violate this prohibition of
Bal Tosif?  Furthermore, we may ask, how can Chazal
instruct us not to blow the Shofar when Rosh Hashanah falls
out on Shabbat?  Does this not violate Bal Tigra?
The Rashba teaches that the Mitzvah applies only
to an individual, because on his own he will come to do
absurd things.  For example, one might think it is a good idea
to wear Tefillin on Shabbat, but even though he may have
the best intentions, he is starting down a slippery slope, and
hence he violates the prohibition.  Chazal, however, since
they are perceptive enough not to make such mistakes, can
decide to make a decree that adds or detracts in some way.
The ideas of the Duvno Maggid and the Rashba
demonstrate that even though we might have good
intentions, we still must not alter the Torah’s body of Mitzvot. 
Sometimes we feel that it is a good idea to be Machmir on
every single little thing, without consulting our Rav for
guidance.  However, this may lead us to be like the borrower,
to say to ourselves, “It’s too much!  Enough of all of this
adding!”  Eventually, like the borrower, we will come to
detract from our fulfillment of the Mitzvot.  Rav Nachman of
Breslov sagely observed that if we come to be excessively
Machmir upon ourselves, the Mitzvot will become a burden. 
Let us rather follow the Rambam, who develops the concept
in Hilchot Dei’ot that one should keep to the “Shevil
HaZahav,” the “golden” middle path.  In so doing (and by
consulting our Rav), we will prevent ourselves both from
adding and from taking away.