The true explanation is so simple that the real mystery is why no one I have ever heard or read has so clearly stated it.
The certainty of answered prayer as Jesus taught it depended on being within God's will. He perfectly fulfilled God's will, and every request or prayer He asked was granted. Among men, many have attempted to explain God's will, studying the Bible, and much writing and preaching have been devoted to this theme. The rest of us, in praying, begin or end with, "If it be Thy will," as if we cannot be certain of the outcome. Knowing the will of God is the mystery, especially considering the new, difficult, and complicated circumstances we must deal with.
Here's the thing: with earthly parents, their children, as they grow and mature, learn about the values and goals of their parents. They come to know exactly what they can ask of their parents that will be granted. They also learn what not to ask for.
So it is with our Heavenly Father. The better we know Him, what He values and what His goals are - especially for us, individually, the more certain will our request and prayers be granted.
As Jesus taught His disciples to pray in His name, God also grants their requests in Jesus' Name. Jesus was and is the perfect example. Every single request and prayer Jesus asked of the Father was granted. This is because Jesus was continually within God's will. He and the Father are One. We therefore must continue to mature and grow in understanding God's will as shown to us in every Word and Deed that Jesus said and did. We must put on the mind of Christ. We must learn to ask or pray what Jesus would in that circumstance. It will always be what is best for all those involved. Best is always measured according to God's will.
The simplest way to say it would be: God wants all men to accept His offer of love and reconciliation through the forgiveness that the death of Christ accomplished. He then wants His children to grow and mature toward the perfect stature as seen in His Only-begotten Son. He wishes us to continually strive to become more and more like Jesus. He is The Way, the Truth, and the Life. He will always forgive us when we falter, encourage us to keep going, and to never give up, reaching toward the prize of being with Him and the Father.
He will always hear our requests and prayers - and the closer our relationship, the more certain the answers, in Jesus' Name.
This article was written by my father T.O.D. Johnston, who was licensed to preach the Gospel by Paran Baptist Church on May 26, 1979. He has been a student of Scripture since 1972. View more lessons at his Bible Study Lessons page.