Knot Of Tefillin

והסרתי את כפי וראית את אחרי ופני לא יראו.  Rashi says וְרָאִיתָ אֶת אֲחֹרָי – הֶרְאָהוּ קֶשֶׁר שֶׁל תְּפִלִּין.  Why is the knot of the tefillin showed to Moshe Rabbenu?  

The Gemarah Berachot (6a) says in the tefillin of Hashem it says  ומי כעמך כישראל גוי אחד בארץ (some say ישראל some say כישראל, and here) meaning that the tefillin of Hashem contain the message of the greatness of Klal Yisrael.  Hashem is telling Moshe that the way to achieve atonement from sin is to realize that even when a Jew commits a sin, he is still tied and attached to Hashem.  The knot of the tefillin represents this unbreakable bond that exists and that is the place from where teshuva can com from (see Likutay Sichos volume 21.)

This is why the mitzvah of tefillin is given right before yetzias mitzraim (Bo) for as Klal Yisrael were leaving the bonds of servitude they wrapped themselves in a bond to Hashem.   

This idea is brought out in this piece from the sefer Ohelai Yaakov (הוסיאטין) that Rabbenu Tam brought Moshe Rabbenu into the Beit Midrash to concur to his opinion that the tefillin do not have to knotted every day because it was important to know that the kesher, the bond with Hashem is always present he cites one version of the tory, there is another version in which Rabbenu Tam disagrees with Moshe Rabbenu, see here.)