What is the significance of the two letter shins (ש) on tefillin?
One side of tefillin has a regular shin (ש) and the second has four-prongs.
Mi Yodeya is a question and answer site for those who base their lives on Jewish law and tradition and anyone interested in learning more. It only takes a minute to sign up.
Sign up to join this communityFrom here, quoting the Beit Yosef to Orach Chaim 32:
The Verse says, "And all the nations of the land will see that the name of God is called upon you and they will fear you" (Devarim 28:10). The Talmud says that this refers to the the Tefillin Shel Rosh (Tefillin of the Head).
G-d Name, The Tetragramaton, is the numerical value of 300, using the Gematria Method known as AT-BASH:
Yud == Mem (40)
Hey == Tzadi (90)
Vav == Peh (80)
Hey == Tzadi (90)
So the 3 pronged Shin represents G-d's name.
According to the Sefer Mitzvos Gedolos, quoted by the Beit Yosef, the writing in the Luchos (Tablets) were sunken in. If so, a Shin had 4 prongs, and the 4 progned Shin on the Tefillin Shel Rosh commemorates that.
The Talmud (Menachot 35A - page 130 of here) says:
Abaye also said, The shin of the tefillin is a law given to Moses at Sinai
I don't recall where I saw this, but essentially we have ש + ש + ו since the extra head of the Shin is a Vav.
This gives us a gematria of 606.
Now we add the 7 vertical bars that create the 2 Shins.
606 + 7 =613; corresponding to the 613 Mitzvoth.