Then the word of the Lord Almighty came to me: "Ask all the people of the land and the priests, 'When you fasted and mourned in the fifth and seventh months for the past seventy years, was it really for me that you fasted? And when you were eating and drinking, we're you not just feasting for yourselves?
The following is an article from the Quest Study Bible published by Zondervan:
Traditions have great value because they preserve the values and teachings of the past. They remind us of things we might otherwise forget. While living in a foreign land, surrounded by foreign culture and language, the Jews could have easily forgotten the important events of their history. Future generations could have missed out on how significantly God had dealt with their ancestors. But they used rituals and traditions to avoid historical ignorance. They commemorated the past so they would not forget the lessons learned.
Unfortunately, the rituals "fossilized" over time. Eventually, people were celebrating only the form and forgetting the reality behind it. Their fasting appeared meaningful but had no inner substance. When this, or something similar happens, a worship activity becomes an empty ritual, or worse, a ritual with the wrong meaning attached to it. Often this can occur as a slow erosion of values---a process that eventually destroys the good others have endeavored to do.