David Siyum on Mishnayos Moed Katan

Mesechtas Moed Katan discusses Chol Hamoed, the days that come between the first and last Yom Tov days of both Pesach and Sukkos. While these days are not full Yomim Tovim, the Chachomim wanted to make sure that some part of the joy and קדושה of the Yomim Tovim remained. They, therefore, placed limits on the types of work we can do on those days.

The basic rule is that a person should not do work unless he is preventing a loss from happening דבר האבד and it does not require too much work "טירכה"

In addition, if you need to do the work for the benefit of Chol Hamoed or Yom Tov than you can do it but it should be done in an amateur way and not a professional way.

The Chachomim also new that people, knowing they will be on vacation, will wait to take care of their things during Chol Hamoed, so they did not allow that either. meaning, if you had time before Yom Tov to take care of the matter and didn't, then you cannot do it on Chol Hamoed.

Therefore, they said no haircuts, washing cloths or writing on chol Hamoed with certain exceptions.

The Mesechta ends with a discussion about אבילות (what to do when a close relative dies) and the changes made on Chol Hamoed.

The Chachomim did not want to end the Mesechta on a sad note, so they ended with a Pasuk from YESHAYA stating that in the future, Hashem will get rid of death forever.