כל איש ישראל חייב בתלמוד תורה בין עני בין עשיר בין שלם בגופו בין בעל יסורים בין בחור בין זקן גדול אפי' עני המחזר על הפתחים אפילו בעל אשה ובנים חייב לקבוע לו זמן לתלמוד תורה ביום ובלילה שנאמר והגית בו יומם ולילה. (ובשעת הדחק אפילו לא קרא רק ק"ש שחרית וערבית לא ימושו מפיך קרינן ביה) (הגהות מיימוני פ"א וסמ"ג עשין י"ב) ומי שא"א לו ללמוד מפני שאינו יודע כלל ללמוד או מפני הטרדות שיש לו יספיק לאחרים הלומדים: הגה ותחשב לו כאילו לומד בעצמו (טור) ויכול אדם להתנות עם חבירו שהוא יעסוק בתורה והוא ימציא לו פרנסה ויחלוק עמו בשכר אבל אם כבר עסק בתורה אינו יכול למכור לו חלקו בשביל ממון שיתן לו (תא"ו נתיב ב' מש"ס דסוטה):
עד אימתי חייב ללמוד עד יום מותו שנאמר ופן יסורו מלבבך כל ימי חייך וכל זמן שלא יעסוק בתורה הוא שוכח:
Until when is a person obligated to learn? Until the day of his death, as it says "And lest they depart from thy heart all the days of thy life" (Deut 4:9). And as long as one does not occupy himself with Torah he forgets it.
חלקו. עש"ך וה"ה חלק כל דהו אינו יכול למכור. פר"ח בליקוטים:
For that it is also said, a part of one's knowledge he cannot sell.
וא"ר יצחק אם יאמר לך אדם יגעתי ולא מצאתי אל תאמן. פירוש שאומר שיגע ולא מצא כלל והא ודאי שקר ענה דגם שלא יזכה להיות גברא רבא דמחדדן שמעתתיה חריף ומקשה מתון ומסיק מ"מ אם יגע באמת ודאי מצא שיהיה תלמיד חכם פשוט מיהא:
Laboring and not finding (success); it must be a lie! But the answer is that even if one does not merit to be a great man [in Torah] whose words are sharp, deliberate, and conclusive, in any case if he labored for real, he for sure found (success) for he will be a simple Talmud Chacham.
Having discussed the importance of reviewing one’s Torah study, the Gemara relates that Rabbi Perida had a certain student whom he would have to teach four hundred times, and only then would he learn the material, as he was incapable of understanding it otherwise. One day they requested Rabbi Perida’s presence for a mitzva matter after the lesson. Rabbi Perida taught his student four hundred times as usual, but this time the student did not successfully learn the material. Rabbi Perida said to him: What is different now that you are unable to grasp the lesson? He said to him: From the time that they said to the Master that there is a mitzva matter for which he is needed, my mind was distracted from the lesson and every moment I said: Now the Master will get up, now the Master will get up to go and perform the mitzva and he will not complete the lesson. Rabbi Perida said to him: Pay attention this time and I will teach you, and know that I will not leave until you have fully mastered the lesson. He taught him again an additional four hundred times. Due to the merit of Rabbi Perida’s great devotion to his students, a Divine Voice emerged and said to him: Is it preferable to you that four hundred years be added to your life, or that you and the rest of your generation will merit the World-to-Come? He said: I prefer that I and my generation merit the World-to-Come. The Holy One, Blessed be He, said to the angels: Give him both; he shall live a very long life and he and the rest of his generation will merit the World-to-Come.
The Gemara in Megilla 27b recounts that when the students of R' Preida asked him how he got to live so many years. R' Preida said it was because he would always come to the Beit Midrash early. But he didn't know it was also because he taught his student 800 times! Or it could be that he didn't know this until after he lived an extra 400 years. (Teachers who don't give up on their students merit much reward!)
רבנו חננאל על עירובין נ’’ד ב
ר"ע אומר חייב אדם לשנות לתלמידו עד שילמד שנא' ולמדה את בני ישראל.
Rabbeinu Chananel on Eruvin 54b
Rabbi Akiva taught that one is obligated to teach his students until they are taught (i.e. until they understand), as the passuk says "and teach it to the people of Israel" (Devarim 31:19). (Our goal when we educate people in Torah should be to do it all the way, however much time it takes.)
(כג) בֶּן הֵא הֵא אוֹמֵר, לְפוּם צַעֲרָא אַגְרָא:
(23) Ben Hey Hey says: According to the pain is the reward.
(א) בן הא הא אומר לפום צערא אגרא
חתם רבינו הקדוש מסכת זו במאמר זה, דקמ"ל דבין בעסק התורה, או בקיום מצותיה, ובין בתקון מדות הנפש, בכולם כפי הצער שתצטער להשלים את עצמך בהן, כן לפי מדה זו יגדל שכרך. או ר"ל דלפי הטרחה והעמל שתתעמל להשיג החכמה, כן עוד יותר תעשה פרי תבואה, דאין ד"ת מתקיים אלא במי שממית עצמו עליה [כברכות דס"ג ב'], ובמי אתה מוצא חמאת התורה במי שמקיא חלב שינק משדי אמו עליה [שם]. ואז נותנת לו חיים עושר וכבוד, ודבש וחלב תחת לשונה:
Whether in learning Torah, doing mitzvot, or working on his character, due to the pain his merit will increase. Or it is saying that according to the labor and tiresome work that one does to increase in wisdom, for that even more one would see the fruits of his work, as the words of Torah are understood only by those who "die over it" (Berachot 63b) as in whom will you find the "butter of Torah"? In he who "spits out the milk that he nursed from his mother’s breasts over it; (i.e. one who struggles with all his might to study Torah)" (Berachot 63b). And thus it gives him a life of success and honor, honey and milk under words of the Torah.
(ד) מוֹדִים אֲנַחְנוּ לְּפָנֶיךָ ה' אלוקינו ואלוקי אֲבוֹתֵינוּ שֶׁשַּׂמְתָּ חֶלְקֵנוּ מִיּוֹשְׁבֵי בֵּית הַמִּדְרָשׁ, וְלֹא שַׂמְתָּ חֶלְקֵנוּ מִיּוֹשְׁבֵי קְרָנוֹת. שֶׁאָנוּ מַשְׁכִּימִים וְהֵם מַשְׁכִּימִים אָנוּ מַשְׁכִּימִים לְדִבְרֵי תּוֹרָה וְהֵם מַשְׁכִּימִים לִדְבָרִים בְּטֵלִים. אָנוּ עֲמֵלִים וְהֵם עֲמֵלִים. אָנו עֲמֵלִים וּמְקַבְּלִים שָׂכָר וְהֵם עֲמֵלִים וְאֵינָם מְקַבְּלִים שָׂכָר. אָנוּ רָצִים וְהֵם רָצִים. אָנוּ רָצִים לְחַיֵּי הָעוֹלָם הַבָּא, וְהֵם רָצִים לִבְאֵר שַׁחַת. שֶׁנֱאמַר: וְאַתָּה אֱלֹקים, תּוֹרִדֵם לִבְאֵר שַׁחַת--אַנְשֵׁי דָמִים וּמִרְמָה, לֹא-יֶחֱצוּ יְמֵיהֶם; וַאֲנִי, אֶבְטַח-בָּךְ.
(4) We give thanks before You, Lord, our G-d and G-d of our fathers, for you gave us a share among those who sit in the study hall, and not among those who sit on street corners. For we arise early, and they arise early; we arise for words of Torah, and they arise for words of emptiness. We work, and they work; we work and receive a reward, and they work and do not receive a reward. We run, and they run; we run towards eternal life, and they run to a pit of desolation. As it says: (Psalms 55:24) "And You, O Lord, bring them down into a pit of desolation, people of blood and deceit will not live out half of their days; and I, I will trust in You." (We should appreciate the uniqueness of Torah learning whereby we are rewarded for the mere act of study no matter how much we material we get through, as distinct from secular studies, where only the end result matters. This should be reflected in our educational practices, such as reconsidering the use of grades in Judaic Studies classes in Jewish day schools.)
The Gemara offers an alternative explanation of this verse: “Keep silence [hasket] and hear, Israel”; break [kattetu] yourselves over words of the Torah. This is in accordance with the opinion of Reish Lakish, as Reish Lakish said: From where is it derived that matters of Torah are only retained by one who kills himself over it? As it is stated: “This is the Torah: When one dies in a tent” (Numbers 19:14); true Torah study demands the total devotion of one who is willing to dedicate his life in the tent of Torah.
Based on the verse "This is the Torah: When a person dies in a tent, whoever enters the tent and whoever is in the tent shall be unclean seven days" (Bamidbar); we see that "this is the Torah" is said in relation to being in the tent of a dead person, but not in relation to touching a dead person. This is to teach us that the Torah is retained by he who kills himself over the tent of Torah" (i.e. puts much effort into engaging with Torah).
With regard to the beginning of the verse: For the churning of milk brings forth curd; in whom do you find the cream of Torah? With one who spits out the milk that he nursed from his mother’s breasts over it; one who struggles with all his might to study Torah. (Those who find it challenging to learn Torah and do so anyway should earn our highest admiration.)
Rabbi Nachum Rabinovich, Yeshivat Birkat Moshe
A nation that internalizes the Torah's ideas and values slowly builds up immunity against shameful seductions. Over the course of generations, students of Torah develop modes of critical thinking that can slice through issues, distinguishing illusion from reality, imaginings from truth, vain puffery from glorious responses to God's voice. Believers in the Torah build up a stockpile of spiritual strength that enables them to overcome the waves of evil that pound the world and its many internal and external pitfalls. They merit the sobriquet of the nation's father: "Israel – for you have striven with God and with men and have prevailed."111 And that is what the sages meant when they said, "Expound it and be rewarded." Its cultural legacy transmits from generation to generation a set of qualities that characterize this nation. This is not the place to dwell at length on Israel's national character, but there is without doubt a common denominator expressing the traits recognizable in our nation. Traces of those qualities linger even within those who have broken away from the Torah's framework; for at least several generations their hearts remain bound, even in alien environments, to their Jewish sources.
from "III. Study is its Own Reward", http://www.edah.org/backend/JournalArticle/Rabinovitch3_1.pdf