There are several interesting implications to praying for God's will to be done “on earth, as it is in heaven”:
-that God does not get what He wills, that He is less than sovereign.
-that God does not have complete control over earth as He does with heaven.
-that our prayers can somehow add to God's chances of getting His will to come about.
When it comes to the difference between God's sovereign will and preferential will and how they effect human outcomes, we ought to be confused. So what does Jesus mean when He tells us to pray “Thy will be done?”
Jesus offered this same prayer to His Father in the garden, just before dying. When Jesus said “Thy will be done” He was indicating that any other agenda He might have had was to be subject to the agenda of His Father.
I do not understand how the sovereignty of God relates to the free will of man or how a just God can be in control of such an unfair world or why a loving, all-powerful God would bring about so many awful things. But I do know that faith requires me to express the same sentiment as Jesus -even if it should mean my painful death in the greatest injustice that ever took place, I ought to trust God enough to say “Thy will be done.”