The source for wearing Tefillin is found in the book of Exodus 13:9; “These words will be a sign on your arm and a reminder between your eyes, so that G-d’s Torah will be in your mouth; for G-d brought you out of Egypt with a strong arm.”
Two questions arise from this verse. Firstly, how are Tefillin and the Exodus connected? Secondly, how does wearing Tefillin cause Torah to be in our mouths?
Rav Abraham Isaac Kook, the first Ashkenazi Chief Rabbi of Israel (at the time it was still under the British Mandate), was a renowned Torah scholar and is recognized as one of the most influential thinkers in religious Zionism. His works are studied widely to this day especially among the religious Zionist camp in Judaism. The following is his explanation for the two questions presented above.
On the surface, the Exodus of the Jewish people from Egypt can be regarded as a one-off event. An event that was truly miraculous and may therefore be etched always in our national memory. However, the Exodus is actually an on-going process. The miracles performed by G-d openly at the Exodus revealed G-d’s light in the world in a way that is still affecting the world today.
“G-d brought you out of Egypt with a strong arm”- the word for arm in Hebrew, Zero’a is rooted in the Hebrew word zera which means seed. This demonstrates how the revelation at Egypt was a divine seed planted then yet still flowering until this day. As one wraps the Tefillin around the arm, one is reminded of the G-d that is found within that continues to develop and elevate the world around, striving towards the divine perfection.
There is a second metaphor used in the Torah to describe the Exodus from Egypt, “yad chazakah”- G-d’s strong arm. The Jewish people’s liberation from the forty-ninth level of impurity in Egypt required G-d’s strong arm- no divine messenger could be used in this case- G-d’s mighty arm had to pull us out of the deep darkness. When fastening the Tefillin to one’s arm and head one is enabled to transform baseness into something that is strong, vital and beautifully holy.
In the same way that G-d uprooted us from our contamination in Egypt we need to make intense daily efforts to ensure that His Torah is what is guiding our actions and thoughts.
If we truly take a few moments each day before putting on Tefillin to focus on these messages, our performance of this commandment can be transformed from a daily, mindless, almost-second-nature kind of act to an uplifting and empowering experience.
Adapted from http://www.ravkooktorah.org/BO64.htm