Moed Katan, Chapter 1, Mishnah 5:
"Ro'in es hanega'im batechilah lehakel, aval lo lehachmir" - so says Rabbi Meir. The kohen's job was to look at a person who had a nega of tzaraas and determine whether the nega was tamei or tahor. According to Rabbi Meir, on Chol HaMoed the kohen may look at the nega for the first time and rule on its status - but only to be lenient, meaning only when he intends to rule that the nega is tahor. But not to be stringent: if he saw that the nega was tamei, he would withhold the ruling and tell the person, "I will look at you after Yom Tov," delaying the decision.
The basis of Rabbi Meir's position is that the kohen is permitted to delay his ruling and is not obligated to decide. And the reason is this: we do not want a person to become tamei with tzaraas on Chol HaMoed, because he would then have to leave the camp, and this is not a fitting time to be outside the camp.
"VaChachamim omrim: lo lehakel v'lo lehachmir":
The Sages disagree and hold that the kohen may not be lenient and may not be stringent either, meaning that the risk should not be taken. Therefore the kohen does not look at nega'im of tzaraas on Chol HaMoed at all, because from the moment the nega is presented to him he is obligated to rule - tamei or tahor. Perhaps he will be forced to say tamei, and the person will have to leave the camp; better, then, that he not enter into that ruling at all.
Gathering bones on Chol HaMoed:
The Mishnah continues with a matter that was unique to Jews in ancient times. It was the practice to bury the deceased in the ground until the body decomposed, and afterward to take the bones and bury them in burial caves, which served as a sort of family plot. For this reason, bringing a person's ancestors' bones to the family graves, to the plot to which they belong, carried an element of relief and even of joy, as we will see below.
"V'od amar Rabbi Meir: melaket adam atzmos aviv v'imo" - on Chol HaMoed a person may gather the bones of his father or mother from the place where they were buried, and rebury them in the family graves. And the reason is: "sh'simchah hi lo" - because it is a joy for him that his parents' bones now rest in the family plot.
Two explanations have been offered for this:
It is a joy in and of itself, from the very act of bringing the bones to the ancestral graves.
The joy of Yom Tov and Chol HaMoed prevents him from grieving excessively, more than he would ordinarily grieve from such an event.
Rabbi Yosei disagrees and holds that this act is considered mourning, and a person must observe it like one day of shivah, and therefore it should not be done on Chol HaMoed.
"Me'orer al meiso":
The Mishnah deals with a matter called me'orer al meiso, arousing grief over one's deceased. It was customary to hire professional eulogizers, whose job was to arouse the emotions of the listeners. Even a person who had lost his relative long ago would sometimes hire someone to gather around him people who had gone through a similar experience - a sort of ancient support group - so that they could weep together. This is "me'orer adam al meiso."
The Mishnah rules that it is forbidden to bring about this arousal of grief, that is, to hire a person to stir up a group of people to weep together and to listen to the words of the professional eulogizer. And not only that, but even someone who lost his relative recently - which is not the same version of eulogizing someone who died long ago - may not hire a eulogizer for the newly deceased within thirty days of the festival, before Yom Tov has begun.
Two reasons are given for this:
The deceased is not forgotten from the heart for thirty days, and therefore within thirty days a person will still feel sharp pangs of grief when Yom Tov arrives, and we do not want him carrying that grief with him into the festival.
People would set aside money for the needs of Yom Tov, and they were liable to use it up on this expense within thirty days, leaving them without cash for the expenses of the festival.
And along the very same lines: it is told that years ago the stock market in Israel would crash twice a year, before Pesach and before Sukkos, when everyone would withdraw their investments so that they could pay for the festival. So this is not a new idea at all.