What does the Bible say about spiritual fasting?

Scripture teaches that spiritual fasting goes beyond mere physical denial; it is about focusing on the heart and the gospel of Christ rather than outward religious acts. In Isaiah 58, God rejects Israel's superficial fasting practices that seek to impress Him through external shows of piety. Instead, He calls for a fast that frees the oppressed, shares resources with the needy, and serves others in love, emphasizing that true worship and devotion stem from the heart's attitude toward God and His grace.