Like giving and praying, fasting also must be vertical, directed toward God and not to impress others. As with the other disciplines, God will reward what He sees, the motives of our heart. As giving provides an opportunity for us to measure our commitment to God, fasting gives us an opportunity to measure the degree to which we value the spiritual more than the physical aspects of our lives. It also demonstrates the sincerity of our prayers.
Scripture References: Matthew 6:16-18