The gemara [ברכות ז] teaches that Hashem showed Moshe the knot of His Tefillin Shel Rosh.
The Rambam in Hilchos Tefillin [3/13] states that it is not possible to explain how the knot of the
Tefillin looks unless one actually sees it [here, a picture says even more than a thousand words]. Maran HaRav Hutner [Maamarei Pachad Yitzchak 88] explains that the source for the Rambam is our gemara where Hashem SHOWED Moshe the knot of His Tefillin.
Gevaldik.
But there is more.
The Brisker Rov [known affectionately as the "Griz"] asked why the Rif quotes this gemara when all the Rif tries to do is teach practical halacha. This gemara is agadic and has no practical import so the Rif should not have mentioned it? Based on what we just learned, says Mo"V HaRav Homnick Shlita, we understand perfectly well what the Rif was trying to teach us. Namely, exactly what the Rambam taught, that one must SEE the knot in order to understand what it looks like.
More gevaldik.
