Those who are serious about prayer and about doing the will of God will use this great prayer aid. It is the best way I know of to detach yourself from earthly, sinful things and to keep your physical appetites under control—so as to prepare your heart for the kind of serious prayer you desire.
Fasting with prayer will cleanse and renews your heart, give you a deep hunger for God, and will make you more sensitive to the things of the Spirit—so that you will be able to understand the deep things of God (1 Cor. 2:10), things that the natural man has no knowledge of (1 Cor. 2:14).
As fasting does its work of cleansing, you will be more and more desirous of prayer—to pray with more earnestness. Continued fasting will help you to express that earnest desire, and at the same time kindle in your soul even more earnest zeal so that you are willing and prepared to continue praying until God gives you the answers you desire.
And fasting not only helps to bring us answers to pressing current problems; it will continue to aid your prayers (and your life). One time of fasting will pay you dividends for a lifetime, even for eternity.
Ronald Dunn, in his book, Don’t Just Stand There Pray Something, writes,
The word Jesus uses for reward [the reward of fasting] in verse 16 [Mathew 6:16, misthon] is different from the one used in verse 18 [apodidomi]. The word used to describe the reward of the hypocrite implies an immediate reward and a reward paid in full. In other words, “What you see is what you get.” But the word Jesus uses to describe the reward given in response to the right spirit [apodidomi] suggests a restoration over a period of time. The rewards of fasting are like dividends from blue chip stock. Day after day, God continues to unfold for you and others the rewards of fasting (p. 168).