The Torah is spiritual. Thus, a person whose deeds are pure and upright and whose intellect spiritual, is able to grasp the entire Torah without forgetting anything. This is because a thing that is spiritual does not take up any space, and so the Torah can expand and reside in his intellect.
But when one imparts corporeality to the words of the Torah and makes them into something palpable, there is then a measure and a limit to how much of it he can grasp in his intellect; [so much,] and no more. And if he wants to perceive more, then that which has already entered his intellect is pushed out. This is like any corporeal thing. If it is already full and one fills it more, that which was already in it is pushed out. This is the cause of forgetfulness.
This is the meaning of: Never let yamush (cease) this book of the Torah—The word yaMuSh has the same connotation as maMaShut (palpability), as it is written (Exodus 10:21), “Vayamesh (And palpable was) the darkness.” That is to say, take care so that there is no palpability and corporeality in the words of the Torah.
This is what our Sages taught (Bava Metzia 85a): “Rav Yosef fasted forty days so that his studies should endure. Of him they declared: ‘It shall not yamush (cease) from your mouth…’ (Isaiah 59:21). He again fasted [forty days], and they declared, ‘… nor from the mouth of your seed.’” That is to say, it should not yamush (become palpable) and become corporeal “from your mouth.” As a result, his studies will endure. For there will be no forgetfulness, because a spiritual thing does not take up any space. Consider the matter well.
לֹא יָמוּשׁ סֵפֶר הַתּוֹרָה הַזֶּה מִפִּיךָ (יהושע א׳:ח׳):
“Lo Yamush (Never let cease) this book of the Torah from your mouth.” (Joshua 1:8)
כִּי הַתּוֹרָה הִיא רוּחָנִיּוּת, וַאֲשֶׁר זַךְ יָשָׁר פָּעֳלוֹ, וְשִׂכְלוֹ רוּחָנִי, יָכוֹל לִתְפֹּס כָּל הַתּוֹרָה כֻּלָּהּ, וְלֹא יִשְׁכַּח דָּבָר. כִּי דָּבָר רוּחָנִי אֵינוֹ תּוֹפֵס מָקוֹם, וִיכוֹלָה הַתּוֹרָה לְהִתְפַּשֵּׁט וְלִשְׁכֹּן בְּשִׂכְלוֹ.
The Torah is spiritual. Thus, a person whose deeds are pure and upright and whose intellect spiritual, is able to grasp the entire Torah without forgetting anything. This is because a thing that is spiritual does not take up any space, and so the Torah can expand and reside in his intellect.
אַךְ מִי שֶׁהוּא מְגַשֵּׁם דִּבְרֵי הַתּוֹרָה וְעוֹשֶׂה מִמֶּנָּה מַמָּשׁוּת, אֲזַי יֵשׁ לָהּ שִׁעוּר וְקִצְבָּה, כַּמָּה הוּא יָכוֹל לִתְפֹּס בְּשִׂכְלוֹ וְלֹא יוֹתֵר. וְאִם יִרְצֶה לְהַשִּׂיג יוֹתֵר, אֲזַי יִדָּחֶה מַה שֶּׁכְּבָר נִכְנַס בְּשִׂכְלוֹ. כְּדֶרֶךְ כָּל דָּבָר גַּשְׁמִי, אִם הוּא כְּבָר מָלֵא, אִם יְמַלְּאֶנּוּ יוֹתֵר יִדָּחֶה מַה שֶּׁהָיָה בּוֹ כְּבָר. וּמִזֶּה בָּא הַשִּׁכְחָה:
But when one imparts corporeality to the words of the Torah and makes them into something palpable, there is then a measure and a limit to how much of it he can grasp in his intellect; [so much,] and no more. And if he wants to perceive more, then that which has already entered his intellect is pushed out. This is like any corporeal thing. If it is already full and one fills it more, that which was already in it is pushed out. This is the cause of forgetfulness.
וְזֶהוּ: לֹא יָמוּשׁ סֵפֶר הַתּוֹרָה. יָמוּשׁ – מִלְּשׁוֹן מַמָּשׁוּת. כְּמוֹ שֶׁכָּתוּב (שמות י׳:כ״א): וְיָמֵשׁ חֹשֶׁךְ. כְּלוֹמַר: הִזָּהֵר שֶׁלֹּא תִּהְיֶה מַמָּשׁוּת וְגַשְׁמִיּוּת בְּדִבְרֵי הַתּוֹרָה.
This is the meaning of: Never let yamush (cease) this book of the Torah—The word yaMuSh has the same connotation as maMaShut (palpability), as it is written (Exodus 10:21), “Vayamesh (And palpable was) the darkness.” That is to say, take care so that there is no palpability and corporeality in the words of the Torah.
מִפִּיךָ – כְּלוֹמַר מֵחֲמַת פִּיךָ, שֶׁיּוֹצֵא מֵאִתְּךָ, יִהְיֶה לָהּ מַמָּשׁוּת וְגַשְׁמִיּוּת, תִּזָּהֵר מִזֶּה.
from your mouth—In other words, because of your mouth. Take care, lest that which comes from you contains palpability and corporeality.
וְזֶה שֶׁאָמְרוּ רַבּוֹתֵינוּ זִכְרוֹנָם לִבְרָכָה (ב"מ פה), שֶׁהִתְעַנָּה רַב יוֹסֵף אַרְבָּעִים יוֹם שֶׁיִּתְקַיֵּם לִמּוּדוֹ. אַחֲווּ לֵהּ: לֹא יָמוּשׁוּ מִפִּיךָ. וְשׁוּב הִתְעַנָּה וְכוּ' אַחֲווּ לֵהּ: וּמִפִּי זַרְעֲךָ וְכוּ'. כְּלוֹמַר שֶׁלֹּא יָמוּשׁוּ וִיגֻשְּׁמוּ מִפִּיךָ, וַאֲזַי יִתְקַיֵּם תַּלְמוּדוֹ, כִּי לֹא יִהְיֶה שִׁכְחָה, כִּי דָּבָר רוּחָנִי אֵינוֹ תּוֹפֵס מָקוֹם, וְדוּק:
This is what our Sages taught (Bava Metzia 85a): “Rav Yosef fasted forty days so that his studies should endure. Of him they declared: ‘It shall not yamush (cease) from your mouth…’ (Isaiah 59:21). He again fasted [forty days], and they declared, ‘… nor from the mouth of your seed.’” That is to say, it should not yamush (become palpable) and become corporeal “from your mouth.” As a result, his studies will endure. For there will be no forgetfulness, because a spiritual thing does not take up any space. Consider the matter well.