This mishnah (chapter 5, mishnah 17; in some versions of the Mishnah it appears as mishnah 20) sets two forms of dispute opposite one another, and teaches us the measuring rod for telling them apart: "Kol machlokes shehi l'shem Shamayim - sofah l'hiskayem, v'she'einah l'shem Shamayim - ein sofah l'hiskayem. Eizo hi machlokes shehi l'shem Shamayim? Zo machlokes Hillel v'Shammai. V'she'einah l'shem Shamayim? Zo machlokes Korach v'chol adaso" - "Every dispute that is for the sake of Heaven will endure in the end, and one that is not for the sake of Heaven will not endure in the end. Which is a dispute for the sake of Heaven? The dispute of Hillel and Shammai. And one that is not for the sake of Heaven? The dispute of Korach and his entire assembly."
The two kinds of dispute:
"Machlokes shehi l'shem Shamayim" - a dispute whose every motive is for the sake of the values of Heaven and the values of Torah: clarifying the truth, seeing justice done, and the like.
"Machlokes she'einah l'shem Shamayim" - a dispute that is really about the person himself: personal ego, the drive to prove that he is right, and the ambition to dominate others.
Two explanations of the words "sofah l'hiskayem":
The Bartenura brings two straightforward readings of the mishnah:
The first explanation - the dispute itself will endure: a dispute that is for the sake of Heaven remains in existence forever. Even once it has been decided, and one side was right while the other was mistaken, since it was a sincere discussion whose entire purpose was to arrive at the truth, even the side that did not prevail is worth weighing and studying. A dispute that is not for the sake of Heaven, by contrast, does not endure in the end: either it disappears, or the people spreading it disappear.
The second explanation - the goal of the dispute will be achieved: "sofah" in the sense of purpose and goal (as the mappik in the hei indicates). One who argues in order to clarify the truth will in the end succeed in finding the truth; whereas one who argues not for the sake of the truth will see his agenda of advancing himself fall flat on its face.
The examples given in the mishnah:
Hillel and Shammai disagreed, and so did their study halls, Beis Hillel and Beis Shammai. Even though the halachah was decided almost always like Beis Hillel, we still take the opinion of Beis Shammai into account and seek to understand their point of view, because it is not there for nothing. And the proof that this was a dispute for the sake of Heaven is that the dispute was never about them personally: they got along with one another, trusted one another, and married into one another's families. It was not a matter of ego, nor a question of who is right, but a sincere attempt to reach the truth. According to the second explanation: in the end they did in fact reach the truth, we have a ruling in halachah, there is mutual respect, and there is one way of conduct in Israel to this day.
Korach and his assembly, by contrast, all died. We do not take their side of the story into account, and they were swallowed up by the earth and are gone. Their goal, to overturn the order of hierarchy in the Jewish people and to a certain extent to depose Moshe Rabbeinu, was crushed and never came about.
The practical message:
Dispute has value. It is a fundamental value in Jewish society and in the spirit of Judaism. But the dispute has to be conducted for the sake of Heaven and for the right reasons: for the sake of the values of the Torah, in order to understand the truth and arrive at it, and in order to ensure that justice is done.
Here great care is needed, because every person claims that he is disagreeing on principle: "It has nothing to do with me, I gain nothing from this, it is a matter of principle." Korach too, presumably, would have said that his dispute was for the sake of Heaven. It is therefore incumbent upon a person to verify that his "for the sake of Heaven" really is for the sake of Heaven, and that the matter has nothing to do with him at all.
Two tests for clarifying one's motive:
The hostility and ego test: If there is personal hostility toward the other side, anger or ill will - that is a very bad sign. And not only that: it is enough that the ego is involved even slightly for the dispute to end up revolving around the person himself - and that is not desirable.
The neighbor test: A person should ask himself - if the matter did not concern him but his neighbor, would he wage the same battle? Would he raise the same arguments? Would he feel it with such intensity? If the fight is over the principle, it should make no difference whether it happened to him or to his neighbor. And if the answer is no - that is a sign that the anger stems from the fact that it happened to him, to his child or to his friend.
Our Sages of blessed memory emphasize again and again how terrible dispute is, and how a dispute in the home, in the shul and in the community leads to the most terrible things. Therefore a person must try his very best to avoid dispute. And if he cannot, because a principle must be upheld and for the sake of Heaven he must take up the matter - fine; but it must be done in a way that is completely free of ego.
Even though anything the Torah values is worth fighting for, it is not worth fighting for once the fight turns into an emotional quarrel and a quarrel of ego. A person is obligated to stand up for justice and truth and to pursue them; but from the moment the ego gets involved, and the matter becomes personal, and a person becomes irritated and angry at his opponent - it is better for him to withdraw and not to have the quarrel at all, even if that means giving up standing up for a value. For once the ego is involved, it is not for the sake of Heaven, and only bad things will come of it.
In summary: In this mishnah we learned the distinction between a dispute for the sake of Heaven and a dispute that is not for the sake of Heaven, and the two explanations of "sofah lehiskayem" - that the dispute itself will endure and be weighed for generations, or that its purpose will be realized. Hillel and Shammai on one side, and Korach and his assembly on the other, are the clearest examples of the two paths. The practical message: dispute is a value, but only when it is clean of ego and personal hostility, and a person must examine himself with the ego test and with the neighbor test. And when the examination does not hold up - giving up the dispute is itself more for the sake of Heaven than fighting for the sake of Heaven.