Musar do Kapłańska 20:2

מועדי ה' אשר תקראו אותם מקראי קודש אלה הם מועדי . The thrust of the legislation is that the בית דין proclaims the dates when the various festivals are to be observed (23,2). You determine when to rejoice, when to eat festive meals. These festive meals should serve a spiritual purpose, just as did the delicacies Isaac ordered before blessing his son. When one approaches the חגים, Holidays, in this spirit, the second half of the verse אלה הם מועדי, "These are My festivals," will be true. If, however, these days are observed only as days when you fill your stomachs, indulge your body, then they are not "My festivals," but are vomit, excrement, concerning which the prophet has quoted G–d as saying: מועדיכם שנאה נפשי, "My soul hates your festivals” (Isaiah 1,14). I have discussed this at greater length in my treatise about the laws applicable to festivals.