Imam ‘Ali (a.s.) said:
إنّما هُوَ عِيْدٌ لِمَنْ قَبِلَ اللّهُ صِيامَهُ وَ شَكَرَ قِيامَهُ وَ كُلُّ يَوْم لايُعْصَى اللّهُ فِيهِ فَهُوَ عَيْدٌ
The day of feast following the month of fasting is the feast for those whose fasts are accepted and their worship is favored by God, and any day in which you do not commit a sin, is the day of feast (Eid). 1
Feast and happiness after one month of fasting in the blessed month of Ramadan is actually the feast of overcoming sensual desires, and of obedience of God’s command. Thus, this is a day of feast only for those who have been victorious in fulfilling this great divine duty and understanding its true philosophy. However, for those shameless people who have not respected this great month and its educational program, it is nothing but a day of mourning and disgrace.