The discipline of fasting breaks you out of the world's routine.
When you are hunger for God, He will fill you.
When the Holy Spirit calls your to fast, He is preparing you for what is ahead.
Every deed has a seed. In other words, the deeds you choose to do in this lifetime create a seed for future generations.
Satan gets disturbed -and defeated -when you decide to do more that be a Sunday-morning Christian.
Many times the rewards of fasting come after the fast, though from time to time answers can come during the fast.