John Murray in Redemption Accomplished and Applied wrote the following:
In order to place the doctrine of perseverance in proper light we need to know what it is not. It does not mean that every one who professes faith in Christ and who is accepted as a believer in the fellowship of the saints is secure for eternity and may entertain the assurance of eternal salvation. Our Lord himself warned his followers in the days of his flesh when he said to those Jews who believed on him, “If ye continue in my word, then are ye truly my disciples, and ye shall know the truth, and the truth shall make you free” (John 8:31, 32). He set up a criterion by which true disciples might be distinguished, and that criterion is continuance in Jesus’ Word (pp. 151–52.)
The above explanation by Murray of the doctrine of perseverance is an elaboration of what Peter meant by his words “protected by the power of God” when he wrote his first epistle (1 Peter 1:5). If any biblical character was ever prone to failure, it was Simon Peter. Judging from the biblical record, none of the Lord’s disciples—excluding Judas the betrayer—stumbled more often or more miserably than he. Peter was the disciple with the foot-shaped mouth. He seemed to have a knack for saying the worst possible thing at the most inappropriate time. He was impetuous, erratic, vacillating—sometimes cowardly, sometimes weak, sometimes hotheaded. On several occasions he merited strong rebukes from the Lord, none more severe than that recorded in Matthew 16:23: “Get behind Me, Satan! You are a stumbling block to Me; for you are not setting your mind on God’s interests, but man’s.” That occurred almost immediately after the high point in Peter’s experience with Christ, when Peter confessed, “Thou art the Christ, the Son of the living God” (Matthew 16:16).
Peter’s life is proof that a true believer’s spiritual experience is often filled with ups and downs, but Peter illustrates another biblical truth, a more significant one: the keeping power of God. On the night Jesus was betrayed, He gave Peter an insight into the behind-the-scenes spiritual battle over Peter’s soul: “Simon, Simon, behold, Satan has demanded permission to sift you like wheat; but I have prayed for you, that your faith may not fail” (Luke 22:31–32, emphasis added).
Peter was confident of his willingness to stand with Jesus, whatever the cost. He told the Lord, “Lord, with You I am ready to go both to prison and to death” (Luke 22:33). Yet Jesus knew the truth and sadly told Peter, “The cock will not crow today until you have denied three times that you know Me” (Luke 22:34).
Did Peter fail? Yes, miserably. Was his faith overthrown? Never. Jesus Himself was interceding on Peter’s behalf, and His prayers did not go unanswered.
The Lord intercedes for all genuine believers that way. John 17:11 gives a glimpse of how He prays for them: “I am no more in the world; and yet they themselves are in the world, and I come to Thee. Holy Father, keep them in Thy name, the name which Thou has given Me, that they may be one, even as We are.”
I do not ask Thee to take them out of the world, but to keep them from the evil one. They are not of the world, even as I am not of the world. Sanctify them in the truth; Thy word is truth. As Thou didst send Me into the world, I also have sent them into the world. And for their sakes I sanctify Myself, that they themselves also may be sanctified in the truth. I do not ask in behalf of these alone, but for those also who believe in Me through their word; that they may all be one even as Thou, Father, art in Me, and I in Thee, that they also may be in us; that the world may believe that Thou didst send Me. And the glory which Thou has given Me I have given to them; that they may be one, just as We are one; I in them, and Thou in Me, that they may be perfected in unity, that the world may know that Thou didst send Me, and didst love them, even as Thou didst love Me (John 17:15–23).
Notice what the Lord was praying for: that believers would be kept from the power of evil; that they would be sanctified by the Word; that they would share His sanctification and glory; and that they would be perfected in their union with Christ and one another. He was praying that they would persevere in the faith.
Was the Lord praying for the eleven faithful disciples only? No. He explicitly includes every believer in all succeeding generations: “I do not ask in behalf of these alone, but for those also who believe in Me through their word” (John 17:20). That includes all true Christians, even in the present day!
Moreover, the Lord Himself is continuing His intercessory ministry for believers right now. “He is able to save forever those who draw near to God through Him, since He always lives to make intercession for them” (Hebrews 7:25). The King James Version translates Hebrews 7:25 thus: “He is able also to save them to the uttermost that come unto God by him, seeing he ever liveth to make intercession for them.”