1 John 5:14-15 (English Standard Version)

 And this is the confidence that we have toward him, that if we ask anything according to his will he hears us. And if we know that he hears us in whatever we ask, we know that we have the requests that we have asked of him.

We have to know His will in order to pray His will.

Since His will is absolute and does not change, praying does not change what God has already done.

Seeing God’s will done because we prayed to see it confirms that we heard God correctly when He revealed His will to us in time. 

Remember that Jesus prayed “If it be thy will, remove this cup from me.”

God did not. That should be a sober reminder about praying for our self-interests.