Avos chapter 6, mishnah 5. In some versions this mishnah is still counted as a continuation of mishnah 4, while in others it stands on its own - and it is certainly connected to what came before it. But whereas the previous mishnah dealt with a person's exclusive focus on Torah study at the expense of everything else, here the mishnah teaches that even someone who has already taken upon himself a life of self-sacrifice can still stumble, and he needs to know what else might go wrong, what else might go right, and how to motivate himself properly.
The wrong motivation - greatness and honor:
"Al tevakesh gedulah le'atzmecha" - the motivation for learning Torah and for accepting a life of self-sacrifice should not be a thought such as: "I will be powerful later on, I will be a great rabbi." "Ve'al tachmod kavod" - nor should it be a pursuit of the honor of people who say: "This young man is a talmid chacham, he is an important person." Such Torah is Torah she'lo lishmah, and in practice it is a transgression, and that is not what we are looking for. True, the work always begins that way, but it is not the proper motivation and it is not the direction we are heading in: someone who already holds fast to a commitment to the path of Torah needs to focus on Torah lishmah.
"Yoser milimudecha aseh":
More than a person learns, he should do. This is a return to an earlier mishnah that spoke about one whose deeds exceed his wisdom. And the point is this: even though a person should not be distracted from learning by bodily pleasures - eating, sleeping and idleness, all of which we are prepared to push off - acts of kindness are never pushed off. Rather, a person is obligated to do them even more than his Torah study.
"Ve'al tis'aveh leshulchanam shel melachim":
A person should not covet the table of the wealthy. Someone is a guest on Shabbos in the home of a wealthy man and sees his table set with every fine thing - he should not let that distract him, and he should not think that one day he too will be like them. He should not fix his gaze there and he should not covet it. There is nothing preventing a person from having both tables at once, but it comes at a price, and that price is one we do not want.
"Sheshulchancha gadol mishulchanam" - in any case, the table of the one who learns Torah is greater than theirs. According to Rashi, the reward in the World to Come that he will enjoy far exceeds all the benefit and enjoyment they receive from their physical possessions in this world.
"Vechisrecha gadol mikisram" - even in this world, the crown of a good name of Torah and good deeds that a person wears exceeds any crown they wear as important and wealthy people.
"Vene'eman hu ba'al melachtecha sheyeshalem lecha sechar pe'ulasecha":
And if a person needs a motivation in order to learn and to keep going, let his "she'lo lishmah" be the reward he receives for Torah study. Let him remind himself, promise himself and believe that the Holy One is faithful, and that He can be relied upon to pay a reward for the effort. In other words, although this is still "she'lo lishmah," it is a "she'lo lishmah" on a higher level: not for the sake of honor and power, but out of a desire to do the will of Hashem and to receive reward for doing His will.
In summary: in this mishnah we learned that even someone who has already taken upon himself self-sacrifice for Torah is required to examine his motivations: not greatness and not honor, which are Torah she'lo lishmah; not pushing off acts of kindness, since the deed outweighs the learning; and not craving the table of kings, since the table and the crown of the one who learns Torah are greater than theirs - in the World to Come and in this world. And if a person needs a motivation, let him rely on the faithfulness of the Employer to pay the wages of his labor, for that is a "she'lo lishmah" that is entirely a desire to do the will of the Creator.