1. Matthew 6:16-18
"When you fast, do not look somber as the hypocrites do, for they disfigure their faces to show others they are fasting. Truly I tell you, they have received their reward in full. But when you fast, put oil on your head and wash your face, so that it will not be obvious to others that you are fasting, but only to your Father, who is unseen; and your Father, who sees what is done in secret, will reward you."
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).