What is the Mishnah in Yadiyim talking about when it says writing in "Ashrit" defiles hands ? "catuv Evri" (The ancient script) does not defile?

Question

Does anyone understand this Mishnah?

The Mishnah in Yadiyim 4:5 says writing in "Ashrit" defiles hands but writing in the "catuv Evri" (ancient Hebrew) does not defile , why and what is this ?

תַּרְגּוּם שֶׁבְּעֶזְרָא וְשֶׁבְּדָנִיֵּאל, מְטַמֵּא אֶת הַיָּדַיִם. תַּרְגּוּם שֶׁכְּתָבוֹ עִבְרִית וְעִבְרִית שֶׁכְּתָבוֹ תַּרְגּוּם, וּכְתָב עִבְרִי, אֵינוֹ מְטַמֵּא אֶת הַיָּדַיִם. לְעוֹלָם אֵינוֹ מְטַמֵּא, עַד שֶׁיִּכְתְּבֶנּוּ אַשּׁוּרִית, עַל הָעוֹר, וּבִדְיוֹ: The Aramaic sections in Ezra and Daniel defile the hands. If an Aramaic section was written in Hebrew, or a Hebrew section was written in Aramaic, or [Hebrew which was written with] Hebrew script, it does not defile the hands. It never defiles the hands until it is written in the Assyrian script, on parchment, and in ink.

Answer 1

Proper hand-written scrolls of Tanach actually are ever-so-slightly impure: people had been storing their scrolls with their sanctified produce, but then the rodents going for the latter messed up the former; to avoid this problem, the rabbis declared the scrolls ever-so-slightly impure (i.e. just enough to require you to wash your hands), so you'd store them away from food.

A real Torah or other book-of-Tanach scroll has to be written in the current, block-ish, Hebrew calligraphic script, known as "Ashuri." The paleo script is no longer acceptable for a Torah scroll, ergo one written in that script doesn't do the impurity thing.

Answer 2

It's a measure of qedusha; only canonical texts which are written in their original language, in the proper script, using the proper materials, are qadosh enough to defile hands. By the time of the mishna Ktav Ashurit [=Aramaic block script] was preferred so if you write canonical texts in Ktav Ivri [=paleo-Hebrew] they aren't qadosh enough to defile the hands.

In the Dead Sea Scrolls there are some examples of canonical texts written in Ivri, especially the tetragrammaton, and even today Samaritans write their torah scrolls in a script which more closely resembles Ktav Ivri than any of ours.