by Reb Gutman Locks
Every custom, and certainly all of the laws that have been handed down from generation to generation, are founded on good reason. Even those that we are told are not based on logic have good reason, but whatever logical reason we might think is the reason for them, is not their ultimate reason, which for now is unknown.
The problem is that when traditions are followed without understanding they become mere ritual, or even worse, burdensome. Yet, as soon as we learn the reasons for that practice, doing it becomes an enlightening experience.
For instance, some Chassidim are careful to follow an unusual custom that surprisingly few people are aware of. And even those who do keep this tradition are hard-pressed to give you an answer as to why they do it. At best they might say, "My grandfather taught me to do it."
We all tie the end of the strap that holds the tefillin onto our arm into the shape of the Hebrew letter י (yud). But these Chassidim tie both ends of that strap into this shape! Why?
The knot that holds the tefillin head piece in place is tied in the shape of the Hebrew letter ד dalet. There is also a widely practiced Chassidic custom to tie this knot into a square that actually forms two dalet(s). Few people will be able to explain why they do this. But when we understand why that knot is tied into one or two dalet(s) we see why the hand strap is tied into one or two yud(s).
Those who tie the head strap into one dalet do so because of the shin on the side of the head tefillin. The shin goes with the dalet on the strap in back of the head, and it also goes with the yud tied on the upper arm strap. This spells one of Hashem's names, Shakai. This name is also written on the outside of the mezuzah (doorpost scroll) and refers to Hashem's protection.
But there are two shin(s) on the sides of the head piece, and this is the reason for tying the head strap into a square, and for tying the second yud in the hand strap. The second dalet and the second yud are for that second shin, spelling Shakai again. But, if they do not tie that second yud on the hand strap, they would have only a shin and a dalet formed there. Shin dalet is the Hebrew word for demon!
Now we see the wonderful reason for that second yud being tied into the hand strap. It changes the shin dalet into Shin Dalet Yud.