The Bible says, “The effectual fervent prayer of a righteous man availeth much”. (James 5:16)

How can we be righteous, for the Bible says, "As it is written, There is none righteous, no, not one:" - Romans 3:10

It is by the gospel - the death, burial, and resurrection of Jesus - that we can become righteous.

"For he hath made him to be sin for us, who knew no sin; that we might be made the righteousness of God in him." - 2 Corinthians 5:21

When we repent by turning from sin to Jesus, have our sins washed away by baptism in Jesus name, and receive His Holy Spirit in us, through Jesus we are made righteous. We have crucified and buried our sinful nature and put on Christ. (Acts 2:38, Romans 6:3-6, Romans 14:17)

"For as many of you as have been baptized into Christ have put on Christ." - Galatians 3:27 KJV

Through Christ, our fervent prayers are powerful.

For example,

"And when they had prayed, the place was shaken where they were assembled together; and they were all filled with the Holy Ghost, and they spake the word of God with boldness." - Acts 4:31 KJV (Acts 4:29-31).

"Peter therefore was kept in prison: but prayer was made without ceasing of the church unto God for him." - Acts 12:5 KJV

Peter was miraculously delivered from prison (to the surprise of the praying church). (Acts 12:6-17).

"And at midnight Paul and Silas prayed, and sang praises unto God: and the prisoners heard them." - Acts 16:25 KJV

Paul and Silas were miraculously delivered from jail. (Acts 16:16-40).

A disciple named Tabitha (Dorcas) was sick and died. Peter prayed for her, and she rose from the dead. (Acts 9:36-42).

"But Peter put them all forth, and kneeled down, and prayed; and turning him to the body said, Tabitha, arise. And she opened her eyes: and when she saw Peter, she sat up." - Acts 9:40 KJV

"And it came to pass, that the father of Publius lay sick of a fever and of a bloody flux: to whom Paul entered in, and prayed, and laid his hands on him, and healed him." - Acts 28:8 KJV (Acts 28:7-9).