The passage states that the letters mem and samech in the Torah tablets were miraculously sustained, and that regarding letters whose internal reading differs from external reading, the scribes of old established conventions because the prophets were not permitted to innovate new matters, though they later forgot and had to re-establish these conventions.
עַלּוֹיֵי קָא מְעַלֵּי לֵיהּ, דְּאָמַר רַב חִסְדָּא: מֵ״ם וְסָמֶ״ךְ שֶׁבַּלּוּחוֹת בְּנֵס הָיוּ עוֹמְדִין. אֶלָּא סָתוּם וַעֲשָׂאוֹ פָּתוּחַ — גָּרוֹעֵי קָא מְגָרַע לֵיהּ, דְּאָמַר רַבִּי יִרְמְיָה, וְאִיתֵּימָא רַבִּי חִיָּיא בַּר אַבָּא: מַנְצְפַךְ צוֹפִים אֲמָרוּם. וְתִיסְבְּרָא?! וְהָכְתִיב: ״אֵלֶּה הַמִּצְוֹת״ — שֶׁאֵין הַנָּבִיא רַשַּׁאי לְחַדֵּשׁ דָּבָר מֵעַתָּה! אֶלָּא מִיהְוָה הֲוַאי, מִידָּע לָא הֲוָה יָדְעִין הֵי בְּאֶמְצַע תֵּיבָה הֵי בְּסוֹף תֵּיבָה, וַאֲתוֹ צוֹפִים תַּקְּנִינְהוּ. וְאַכַּתִּי ״אֵלֶּה הַמִּצְוֹת״ — שֶׁאֵין הַנָּבִיא רַשַּׁאי לְחַדֵּשׁ דָּבָר מֵעַתָּה! אֶלָּא, שְׁכָחוּם וְחָזְרוּ וְיִסְּדוּם.
he elevates its status, as Rav Ḥisda said: The letters mem and samekh that were in the tablets were standing miraculously. Each letter was chiseled all the way through the tablets. In that case, the segment of the tablets at the center of the samekh and final mem, letters that are completely closed, should have fallen. Miraculously, they remained in place. Consequently, rendering an open mem closed elevates its status. However, if one rendered a closed letter open, he diminishes its status, as Rabbi Yirmeya said, and some say that it was Rabbi Ḥiyya bar Abba who said: The prophets instituted the difference between the open and closed forms of the letters mem, nun, tzadi, peh, kaf. Since the closed letters date back to the Ten Commandments, apparently the prophets introduced the open versions of the letters, which are therefore less significant. The Gemara rejects this: And is that reasonable? Isn’t it written: “These are the commandments that the Lord commanded Moses to tell the children of Israel at Mount Sinai” (Leviticus 27:34). The word “these” underscores that a prophet is not permitted to introduce any new element related to the Torah and its mitzvot from here on. Rather, the prophets did not innovate these forms. Both the open and closed versions existed before then. However, people did not know which form appeared in the middle of a word and which form at the end of a word. And the prophets came and instituted their set positions. The Gemara asks: And still the question remains: Didn’t the Sages derive from the verse: “These are the commandments,” that a prophet is not permitted to introduce any new element from here on? How could they institute the position of the letters? Rather, over the course of time, the people forgot their positions in the words and the prophets then reestablished their positions. Apparently, closed letters are no more significant than the open ones.