True prayers are like those carrier pigeons that find their way so well: they cannot fail to go to heaven, for it is from heaven that they came. They are only going home.
If we are wholly living unto God, our prayers will run side by side with His purposes, and none of them will fall to the ground.
"Delight thyself also in the LORD; and he shall give thee the desires of thing heart."
"The effectual fervent prayer of a righteous man availeth much"
"If ye abide in me, and my words abide in you, ye shall ask what ye will, and it shall be done unto you."