רש”י כותב (מנחת ל”ד ע”ב) דתפילין של ראש קדושתו חמור משל יד משום
שרובו של שדי נעשה (בקשר) בשל ראש שי”ן דל”ת אבל בשל זרוע אין אלא יו”ד
I dont understand?
If it is the Shin, Daled and Yud are the SHem Hashem, then –
1. It should be ossur to take them apart.
2. We should put them on the other way, The Shin before the yud, because of כסדרן (or, at least you should have to make the Shin & the Daled before making the Yud)
3. In Hil. Shabbos someone who writes two אותיות on tow walls / pages of a book etc. that are נקראים כאחד it is called כתיבה. Here, the letters are not ‘read together’ so how do they add up to become the Shem Hashem?
You cannot say it is all just a רמז, because the Gemoro calls it תורת ד’ בפיך and it is more kodoish (according to Rashi) as a result. See the Brisker Rov Hil Tefillin.
Can anybody help me?