Several preliminary observations before we answer the question of this article.

First, unbelievers can learn about Jesus. That is, they can be involved in following Jesus. Unbelievers can go to church, Sunday school, home Bible studies. They can even go to Bible college or seminary.

We would be foolish to require that someone be a believer in Jesus Christ in order to attend our church or class. (However, it is reasonable to require someone to be a believer in Him in order to attend a theological school since that is a different matter.)

Second, believers should learn more and more about the Lord Jesus from the day we are born again until the day we die or are raptured.

Third, unbelievers and believers can drop out. They can stop coming to our church, Bible study, or discipleship class. The fact that someone drops out does not indicate whether they are born again or not. Anyone who has ever believed in Jesus for everlasting life is eternally secure (John 3:16; 5:24). One need not remain in Christian instruction to retain everlasting life. Of course, if a believer drops out, then he will reap the consequences. Painful consequences. Until he repents and gets back in Christian instruction.

Fourth, if someone has not been baptized as a believer, then he is really not a disciple of Jesus in the way Luke uses the expression in Acts. I realize we have people today who have believed in Jesus and been under Christian instruction for decades, yet have not undergone believer baptism. Some were baptized as babies and figured that was enough. Some had never been baptized and had never been taught its importance (Matt 28:18-20).

The Lord will be gracious at the Bema, and that He will not rebuke harshly the unbaptized Christian who was merely ignorant (Luke 12:47-48). But I imagine there will be some rebuke. We have the Scriptures. We should be baptized.

I was baptized as a baby in the Orthodox Church. I was baptized as a believer at age 20, shortly after I came to faith in Christ. Why? Because I was shown from the Bible that believer’s baptism is the first step in discipleship (Matt 28:18-20).

When I pastored a small church during my doctoral work I baptized a number of people, including one of the elders, his wife, and his two daughters. Eddie had been baptized as a teen in a Baptist church. But he heard me teach on the importance of believer’s baptism and he became convicted. Here is what he told me: “When all the other teenage boys went forward, I did too. For years I figured that I was saved and then baptized. But years later I came to this church and sat under the teaching of David, the pastor before you. Under his teaching I came to believe in justification by faith alone. Before that I’d been fuzzy in my thinking. I guess I figured that committed people went to heaven. But I came to faith under David. Yet I didn’t get baptized because I figured my earlier baptism was enough. Now I realize it was not. So although I’m 45 and an elder, I want to be baptized.”

Fifth, while it is fine to call yourself a disciple of Jesus, it is a bit more accurately Biblically to call yourself a believer, a brother or sister, a follower of Christ, a Christian, or a learner about Christ.

Now to the question addressed in the title.

Paul Beasley-Murray suggests that the reason the Apostles abandoned (to use his word) the term disciple is because “the term ‘disciple’ said too little with regard to horizontal relationships.” He said that they preferred the family term brother(s): “The most common word used as a term of ‘self-designation’ in the New Testament is ‘brothers’ (Greek:‘adelphoi’), which in those days was an inclusive term referring to ‘brothers and sisters.’” See Beasley-Murray’s article here.

That is a super observation. Free Grace people have long said that the term brethren (brothers) refers to born-again people. That term is used fourteen times to refer to the readers of James, for example. But I think we should also say why that term was used rather than some others. All believers are related. Brethren is a relational term.

Bob Deffinbaugh, a wonderful Bible teacher who is an accurate exegete most of the time, deals with this question in a Bible.org article. He mistakenly concludes that salvation from eternal condemnation is achieved by following Christ. He even goes so far as to suggest that what I’m suggesting in this article is “easy believism.”

We are not born again by following Jesus or by being in Christian instruction. There is only one way to be born again: by faith alone in the Lord Jesus Christ. See John 3:14-18; 5:24; 6:35; 11:25-27; Acts 16:31; Rom 4:4-5; Eph 2:8-9; 1 Tim 1:16; Rev 22:17.

Good intentions are not enough. Going to church is not enough. Indeed, if we think that we will make it to heaven because of our commitment, our following, and our obedience, then we do not believe the one and only message of life.

Deffinbaugh does, however, rightly suggest that discipleship in the Gospels referred to something different than what happens today when elders teach believers today. Discipleship today is primarily corporate, taking place in the local church.

So why isn’t the word disciple used in the epistles? 1) Probably because brethren is a relational word. 2) Possibly because people can no longer literally follow the Lord Jesus or His Apostles. By reserving the term disciple to those who followed Jesus (Matthew, Mark, Luke) and possibly to those who followed the Apostles (Acts), we recognize that the church is “built on the foundation of the apostles and prophets, Jesus Christ Himself being the cornerstone” (Eph 2:20). 3) Definitely because the Holy Spirit for some unstated reason preferred adelphoi (brethren) to mathētai(disciples) as a designation for believers today.