Deuteronomy 14 - 16

The nation of Israel would demonstrate their devotion to God in every avenue of their society.  Even such "normal" activities as mourning for the dead, foods enjoyed, giving of sacrifices, charitable giving, personal debt and employment practices were to be conducted in such a way that it would be very clear that they were submissive to God and His directions.  The celebrations of the national festivals were reviewed so that the nation would remember their significance.