417. Writing Shad-dai
Tefillin, Mezuzah v’Sefer Torah 5:4
The common practice is to write Shaddai (“Almighty,” a Name of God) on the outside of a mezuzah, opposite the empty space between the two sections. This does not affect the validity of the mezuzah because it is written on the outside. However, if one writes the names of angels, other holy names, Biblical verses, etc. on the inside of a mezuzah, he does not have a share in the Next World. Not only does such a person cancel out the mitzvah, he turns it from a sign of God’s unity and our love for Him into some kind of good luck charm. In his foolishness, he actually thinks that this will help him.
Tefillin, Mezuzah v’Sefer Torah 5:5
There is a mitzvah to write the words “al ha'aretz” on the last line of the mezuzah, either at the beginning or in the middle of the line. The universal practice has become for scribes to write mezuzos with 22 lines with the words “al ha'aretz” at the start of the last line. The letters that appear at the start of each line are: Shema, the Tetragrammaton (YHVH), hadevarim, l'vanecha, u’v'shochb’cha, bein, v'haya, m'tzaveh, b'chol, yoreh, eisev, pen, v'hishtachavisem, hashamayim, va'avad'tem, v'samtem, osam, osam (again), baderech, u’visharecha, asher, and al ha'aretz.