Sifrei Devarim 160

¹(Devarim 17:18) "And it shall be when he shall sit on the throne of his kingdom": If he does all that is written in this regard, he is worthy of sitting on the throne of his kingdom. ²"that he shall write for himself the mishneh of this Torah": expressly for himself; he is not to "bedizen" himself with those of his ancestors. " ³mishneh ": This tells me only of mishneh Torah ("the repetition of the Torah," i.e., the book of Devarim). Whence do I derive (that the mitzvah applies also) to the rest of the Torah? From ( Ibid . 19) "to heed all the words of this Torah." If so, why is it written "the mishneh of this Torah"? Because it (i.e., the script) is destined to change (viz. Ezra 4:7 and Daniel 5:8). ⁴Others say: On the day of Hakhel (viz. Ibid . 21:12) only mishneh Torah (Devarim) is to be read (and it is to this Hakhel reading that our verse is alluding.) ⁵"on a scroll": and not on a tablet and not on paper, but only on a megillah (a scroll). ⁶"before the Cohanim, the Levites": from the scroll in the azarah (the Temple court).