There is one other great and eternal truth about prayer that cannot be emphasized too strongly. It is that if there had been no atonement of Christ; if the Son of God, in whose name we pray, had not ransomed man from the fall; if he had not put the great plan of redemption into operation by the shedding of his blood—except for these things, prayer in his name or any name, offered to the Father or any other person or thing, would be of no avail. Prayer is efficacious because of the atonement. As we have repeatedly pointed out in other connections, if there had been no atonement, the Father’s plan would have been frustrated and all his purposes, including the reason for creation itself, would have become void.
Bruce R McConkie, "Promised Messiah"