Fasting
In Isaiah 58, fasting is used as a symbol of religious devotion that, when done hypocritically, is empty and displeasing to God. The people fast for their own benefit and not in a way that aligns with God's desires.
This symbol highlights the importance of sincerity in worship and the need for true repentance and justice, rather than mere ritualistic observance.
Fasting was a common practice in ancient Israel, often associated with mourning, repentance, and seeking God's favor.