Answer: The prayer of a righteous person is powerful and effective, (verse 16).
MORE INFORMATION AND/OR OTHER SCRIPTURE REFERENCES:
The King James Version of the Bible translates "powerful and effective" as "availeth much." The word "availeth" here means "to have force" or "to be of strength." The word "much" means "plenteous, abundant, much." Thus, the New International Version translates this as "powerful and effective." One could say that "the prayer of a righteous person has abundant (or much,) force (or strength)." God listens to and hears His children, and He is powerfully effected by their prayers:
Psalm 17:6: "I call on you, O God, for You will answer me; give ear to me and hear my prayer."
Matthew 7:7-12: [Jesus said,] "Ask and it will be given to you; seek and you will find; knock and the door will be opened to you. For everyone who asks receives; he who seeks finds; and to him who knocks, the door will be opened. Which of you, if his son asks for bread, will give him a stone? Or if he asks for a fish, will give him a snake? If you, then, though you are evil, know how to give good gifts to your children, how much more will your Father in heaven give good gifts to those who ask Him! So in everything, do to others what you would have them do to you, for this sums up the Law and the Prophets."
John 9:31: "We know that God does not listen to sinners. He listens to the godly man who does His Will."
1 John 5:13-15: "I write these things to you who believe in the Name of the Son of God so that you may know that you have eternal life. This is the confidence we have in approaching God: that if we ask anything according to His Will, He hears us. And if we know that He hears us--whatever we ask--we know that we have what we asked of Him."
