“Where did the 4-pronged letter Shin in the tefillin shel rosh come from?”
The answer to that is a Dvar Torah which I heard, which I will try to summarise:
We learn in Masechtes Chagiga that before the Churban there were either 600 or 700 sedorim of Mishnayos(Machloikes).
We also knoew that in Shomayim/Oilom Haboh we are said to have two crowns. One to represent Tefillin(Shel Rosh) and the other to represent Mishnayos.
The Shin’s on the Teffilin shel Rosh represent this.
The Gematria of two shins (each with 3 lines(total of 6)) is 600 , keneged the 600 sedorim of mishnayos we had.(The extra line in the second makes 7 lines representing the other shitah of 700 sedorim).
However, now that sadly we don’t have the Beis Hamikdosh any more, we went from 600 or 700 down to 6 sedorim. Two Shin’s put next to each other is the word “שש” which gets translated to 6.
Please remember this is a short summary of a 15-20 minute shuir on this topic.
IY”H Moshiach should come now and we will be able to see the Beis Hamkidosh with our own eyes.