Do Calvinists believe in “once saved, always saved”, as many evangelicals do? Or can one “fall off the wagon” and lose their salvation, despite a conversion earlier in life? If one’s salvation can be lost, then how does that jive with predestination?
Once saved, always saved. In the TULIP, it is point 5: Perseverance of the Saints. God perseveres with us and drags us into heaven.
There are many, many Scriptures to support this including, “For I am confident, that He who began a good work in you will perfect it until the day of Christ Jesus.”
Yes, a Calvinist believes that once (truly) saved, always saved. Usually called “Perseverance of the Saints.”
If someone falls permanently off the wagon, so to speak, and loses his salvation, so to speak, we assume he was never saved to begin with, but was deceiving himself and/or others (not God, God is never fooled).
I was writing what I thought was an adequate explanation of this belief, and searched for a particular scripture verse online - and came upon the following by John MacArthur, so I will defer to a mind and ministry far greater than mine!:
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” (emphasis added).
He continues:
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” (v. 20). That includes all true Christians, even in the present day!