Jesus assumes His followers will fast ("when you fast," not "if"), making fasting normative for believers. He contrasts hypocritical fasting for human approval with sincere fasting for God alone.
The Pharisees fasted twice weekly (Luke 18:12) and made their fasting conspicuous through ashes, unwashed faces, and mournful expressions. Jesus commands the opposite: normal appearance while fasting, keeping the discipline between the believer and God.
The promise of the Father's reward emphasizes that genuine fasting focuses on relationship with God, not religious performance. This teaching revolutionized fasting from external ritual to internal devotion (BibleHub Commentaries).
