"And whatever you ask in My name, that I will do, that the Father may be glorified in the Son. If you ask anything in My name, I will do it." - John 14:13-14 (KJV)
In all our praying, however, it is important that we keep in mind that God will not alter His eternal purposes at the word of a man. We do not pray in order to persuade God to change His mind. Prayer is not an assault upon the reluctance of God, nor an effort to secure a suspension of His will for us or for those for whom we pray.
Prayer is not intended to overcome God and "move His arm." God will never be other than Himself, no matter how many people pray, nor how long nor how earnestly.
God's love desires the best for all of us, and He desires to give us the best at any cost. He will open rivers in desert places, still turbulent waves, quiet the wind, bring water from the rock, send an angel to release an apostle from prison, feed an orphanage, open a land long closed to the gospel.
All these things and a thousand others He has done and will do in answer to prayer, but only because it had been His will to do it from the beginning. No one persuades Him.
What the praying man does is to bring his will into line with the will of God so God can do what He has all along been willing to do. Thus prayer changes the man and enables God to change things in answer to man's prayer.
from The Price of Neglect, pp. 51-52