B. Spiritual Level of Chol Hamoed-Chulin Al Taharas Kodesh:^[1]

The days of Chol Hamoed are unique in the Jewish calendar, as they are partially holy but remain partially mundane. The reason for this is as follows: There exist two forms of weekdays. One form of weekday is a day which is completely mundane and corresponds to the chambers of the evil of Noga. The second is a weekday that is built upon holiness and contains a ray from Holiness which penetrates into the mundane weekday. This is the level of Chol Hamoed.

[1] Torah Or 12a