This is explained in the Torah (Exodus 17:14): “God said to Moshe, ‘Write this as a reminder in the book, and repeat it in Yehoshua’s ears.’” For even though He said to write it in the book, He was not satisfied with this. He commanded him: “and repeat it in Yehoshua’s ears.” [Moshe was] to speak to him face-to-face. For the main thing is that which we hear directly from the tzaddik.
This is as the Midrash (Devarim Rabbah 3:10) teaches on the verse “Listen, Israel, today you are crossing the Jordan” (Deuteronomy 9:1). It says: What caused him to say to them here, “Listen, Israel”? The Rabbis say: This can be compared to a king who betrothed a matron by giving her two pearls. When she misplaced one of them, the king said to her, “You lost one, take care of the other.” Similarly, the Holy One betrothed Israel with “we will do and we will hear” (Exodus 24:7). They lost the “we will do” by making the Golden Calf. Moshe said to them, “You’ve lost ‘we will do,’ take care of ‘we will hear.’” Hence, “Listen, Israel.” To here the text of the Midrash.
Therefore, when one studies from a book—an aspect of doing, corresponding to “we will do”—it does not have that much power to arouse him. This is because Israel lost the “we will do.” But when he hears directly from the tzaddik, it corresponds to “we will hear.” This crown remained with them, with Israel, as above.
הָעִנְיָן מַה שֶּׁצְּרִיכִין לִנְסֹעַ לְהַצַּדִּיק, וְלֹא דַּי בְּסִפְרֵי מוּסָר,
Regarding the matter of having to travel to the tzaddik, it not being sufficient [to study] ethical works:
מְפֹרָשׁ בַּתּוֹרָה (שמות י״ז:י״ד): וַיֹּאמֶר ה' אֶל מֹשֶׁה כְּתֹב זֹאת זִכָּרוֹן בַּסֵּפֶר וְשִׂים בְּאָזְנֵי יְהוֹשֻׁעַ; כִּי אַף שֶׁאָמַר לוֹ לִכְתֹּב בַּסֵּפֶר, אַף עַל פִּי כֵן לֹא הִסְתַּפֵּק בָּזֶה, וְצִוָּה לוֹ: וְשִׂים בְּאָזְנֵי יְהוֹשֻׁעַ – שֶׁיְּדַבֵּר עִמּוֹ פֶּה אֶל פֶּה. כִּי הָעִקָּר – מַה שֶּׁשּׁוֹמְעִין מִפֶּה הַצַּדִּיק,
This is explained in the Torah (Exodus 17:14): “God said to Moshe, ‘Write this as a reminder in the book, and repeat it in Yehoshua’s ears.’” For even though He said to write it in the book, He was not satisfied with this. He commanded him: “and repeat it in Yehoshua’s ears.” [Moshe was] to speak to him face-to-face. For the main thing is that which we hear directly from the tzaddik.
וּכְמוֹ שֶׁאָמְרוּ בַּמִּדְרָשׁ (דברים ג׳:כ״א) עַל פָּסוּק: שְׁמַע יִשְׂרָאֵל הַיּוֹם אַתָּה עוֹבֵר אֶת הַיַּרְדֵּן וְכוּ', וְזֶה לְשׁוֹנוֹ: מָה רָאָה לוֹמַר לָהֶם כָּאן "שְׁמַע יִשְׂרָאֵל", רַבָּנִין אָמְרִי: לְמָה הַדָּבָר דּוֹמֶה, לְמֶלֶךְ שֶׁקִּדֵּשׁ מַטְרוֹנָה בִּשְׁנֵי מַרְגָּלִיּוֹת, אִבְּדָה אַחַת מֵהֶן. אָמַר לָהּ הַמֶּלֶךְ: אִבַּדְתְּ אַחַת, שִׁמְרִי אֶת הַשְּׁנִיָּה. כָּךְ קִדֵּשׁ הַקָּדוֹשׁ־בָּרוּךְ־הוּא אֶת יִשְׂרָאֵל בְּנַעֲשֶׂה וְנִשְׁמַע, אִבְּדוּ אֶת נַעֲשֶׂה, שֶׁעָשׂוּ אֶת הָעֵגֶל, אָמַר לָהֶן מֹשֶׁה: אִבַּדְתֶּן נַעֲשֶׂה, שִׁמְרוּ נִשְׁמַע, הֱוֵי: שְׁמַע יִשְׂרָאֵל. עַד כָּאן לְשׁוֹן הַמִּדְרָשׁ.
This is as the Midrash (Devarim Rabbah 3:10) teaches on the verse “Listen, Israel, today you are crossing the Jordan” (Deuteronomy 9:1). It says: What caused him to say to them here, “Listen, Israel”? The Rabbis say: This can be compared to a king who betrothed a matron by giving her two pearls. When she misplaced one of them, the king said to her, “You lost one, take care of the other.” Similarly, the Holy One betrothed Israel with “we will do and we will hear” (Exodus 24:7). They lost the “we will do” by making the Golden Calf. Moshe said to them, “You’ve lost ‘we will do,’ take care of ‘we will hear.’” Hence, “Listen, Israel.” To here the text of the Midrash.
וְעַל כֵּן כְּשֶׁלּוֹמֵד מִתּוֹךְ הַסֵּפֶר, שֶׁהוּא בְּחִינַת עֲשִׂיָּה, שֶׁהוּא בְּחִינַת נַעֲשֶׂה, אֵין בָּזֶה כֹּחַ כָּל כָּךְ לְעוֹרֵר אוֹתוֹ, כִּי יִשְׂרָאֵל אִבְּדוּ אֶת הַנַּעֲשֶׂה. אֲבָל כְּשֶׁשּׁוֹמֵעַ מִפֶּה הַצַּדִּיק, הוּא בְּחִינַת נִשְׁמַע, שֶׁזֶּה הַכֶּתֶר נִשְׁאָר לָהֶם לְיִשְׂרָאֵל כַּנַּ"ל:
Therefore, when one studies from a book—an aspect of doing, corresponding to “we will do”—it does not have that much power to arouse him. This is because Israel lost the “we will do.” But when he hears directly from the tzaddik, it corresponds to “we will hear.” This crown remained with them, with Israel, as above.