What then is a true disciple? Or what does Jesus mean by saying in verse 31, “you are truly my disciples”? Let’s be really clear here: For Jesus “true disciple” is the same as “true Christian” or “true believer.” Jesus is not saying that “true disciple” is a second stage in the Christian life. First believer, and then later you attain the level of disciple.
There have been ministries who talk that way. First, you’re an unbeliever, then you are a believer, then you grow into a disciple, and then you are a disciplemaker. That is not the way Jesus thought. And one piece of evidence for saying this is to notice the words he uses here in verse 31: “Jesus said to the Jews who had believed in him, ‘If you abide in my word, you are truly my disciples.” He did not say to these professing believers, “If you abide in my word, you will become truly my disciples.” In other words, he did not teach that being a true disciple was a later stage after simple belief. No. He said, “If you abide in my word, you are truly my disciples.” Now that you have believed, here is how you can know what you now are. You can know if your belief is real: You are now my true disciples if you go on abiding in my word.
So there is no thought here about “true discipleship” being a second stage of Christian maturity. True disciple means true believer or true Christian or true follower. It means, for example, truly forgiven for your sins. Look at verse 24: “I told you that you would die in your sins, for unless you believe that I am he you will die in your sins.” So he says, if you do believe in me, you won’t die in your sins.
John Piper, Sermons from John Piper (2000–2014) (Minneapolis, MN: Desiring God, 2014).