The straps that emanate from the tefillin emanate to the right and the left. The straps then hang down, showing the involvement of this Divine intervention and supervision all the way down through history. In the intertwining of a knot, some straps are revealed and others are covered. Moshe was troubled by the seeming injustice in the world. Hashem showed him that nothing is haphazard.
Nothing happens by chance.
Every event is the practical application of the Divine will and purpose. As such, every event is justice as it is comprised of the union of chessed and gevurah. Hashem showed him the knot of his tefillin.