Three mitzvos that have a unique ability to prevent sin.
The next tool Hashem gave us to fight the Yetzer Hara is His זְרֹעַ נְטוּיָה – outstretched arm. This is the first of three weapons a person can gird to fight his evil inclination. The Gemara (Menachos 43b) says:
רַבִי אֱלִיעֶזֶר בֶן יַעֲקֹב אוֹמֵר כֹל שֶיֵּש לוֹ תְפִילִין בְרֹאשוֹ וּתְפִילִין בִזְרוֹעוֹ וְצִיצִית בְבִגְדוֹ וּמְזוּזָה בְפִתְחוֹ הַכֹל בְחִיזּוּק שֶלֹא יֶחֱטָא שֶנֶאֱמַר וְהַחוּט הַמְשוּלָש לֹא בִמְהֵרָה יִנָתֵק וְאוֹמֵר חוֹנֶה מַלְאַךְ ה' סָבִיב לִירֵאָיו וַיְחַלְצֵם - Rabbi Eliezer ben Ya’akov says: Anyone who has tefillin on his head, tefillin on his arm, tzitzis on his garment, and a mezuza on his doorway is strengthened from all sides so that he will not sin, as it is stated in the possuk (Koheles 4:12) “And a threefold cord is not quickly broken”. This is interpreted as an allusion to the three mitzvos of tefillin, tzitzis, and mezuza. And the possuk (Tehillim 34:8) says “The angel of Hashem encamps round about them that fear Him, and delivers them”. This is interpreted to mean that the angel of Hashem surrounds those who fulfill the mitzvot and saves them from sin.
The tefillin on a person’s arm is alluded to by the זְרֹעַ נְטוּיָה – outstretched arm – with these tefillin placed on the arm. The great fear, the מֹרָא גָדֹל of this possuk alludes to the tefillin on a person’s head. The Gemara (Berachos 6a) says on the possuk (Devarim 28:10) וְרָאוּ כָל עַמֵי הָאָרֶץ כִי שֵם ה' נִקְרָא עָלֶיךָ וְיָרְאוּ מִמֶךָ, וְתַנְיָא, רִבִי אֱלִיעֶזֶר הַגָדוֹל אוֹמֵר: אֵלוּ תְפִילִין שֶבָרֹאש - And all the nations of the land shall see that the name of Hashem is called upon you, and they will fear you”. Rabbi Eliezer the Great says: This is a reference to the tefillin of the head, upon which the name of Hashem is written. Everyone who sees a Yid with tefillin on his head is scared of him, as he sees Hashem’s name resting on the head of the person. This is why the tefillin on the head are alluded to with the words מֹרָא גָדֹל.
The tzitizis are alluded to with the word בְאֹתוֹת – with signs. Tzitzis are the sign on the clothing of every member of Klal Yisroel that we are servants of Hashem.
The mezuzah is alluded to with the word בְמֹפְתִים – with wonders. A mezuzah on the door of a house is an announcement that this person living here is a servant of Hashem. It is also a message to the evil forces in the world to ignore this house. The Zohar says that there are many groups of evil klippos that jump back in fear when they see the name of Hashem on the door of a Jewish house.
