What is "Yom Mo'ed"?
Rashi: The day designated for the enemy to come against you.
Radak: The day of the Churban ? "Kol Nasnu b'Veis Hashem k'Yom Mo'ed" (Eichah 2:7).
Malbim: This refers to "Al Yismach Yisrael El Gil ka'Amim" (1). How do you want to rejoice like the nations rejoice on their special days, at the time of harvesting barley and wheat, and when they gather [into the houses]. How can you rejoice ? your grain and wine will not feed you (2)!
What is "Yom Chag Hashem"?
Rashi: The day designated for the enemy to come against you.
Radak: The day of the Churban is called Chag Hashem, for Hashem called the enemies to come together to Beis Hashem to destroy it and spill blood of Bnei Yisrael like blood of Korbanos - "v'Haysah Li ka'Ari'el" (Yeshayah 29:2).
Malbim: It is days of the festival. They used to offer Korbanos and Nechasim. After these ceased, how will you celebrate Chag Hashem?!
