Luke 14:26 "If anyone comes to me and does not hate father and mother, wife and children, brothers and sisters--yes, even their own life--such a person cannot be my disciple [μαθητής].
Why is the word "disciple" rarely used by anyone except by Jesus in the NT? Paul never used the word. As mentioned by one of the comments,the word μαθητής is not in LXX at all.
Matthew 28:19 Therefore go and make disciples of all nations.
First, we must recall that much (not all) of the NT is written and steeped in Hebrew idiom. This an example of Hebrew hyperbole. But let me get to that in a moment. First the meaning of the word, "disciple".
The Greek word μαθητής (mathetes) according to BDAG has two basic meanings:
Note especially that such "disciples" were often martyrs and under such circumstances they clearly valued their faith and trust in Jesus much more than other earthly associations as demonstrated by their willingness to die for their Lord. Indeed, Jesus warned his followers that family members will betray the disciples:
Matt 10:21, Brother will betray brother to death, and a father his child; children will rise against their parents and have them put to death. See also Mark 13:12.
It is in this sense that Jesus, in Luke 14:26, is telling the disciples that they must love Him supremely over all others, using classic Hebrew hyperbole.
Ellicott observes on Luke 14:26,
If any man come to me, and hate not his father.--Like words had been spoken before, as in Matthew 10:37-39, where see Notes. Here they appear in a yet stronger form, "not hating" taking the place of "loving more," and they are spoken, not to the Twelve only, but to the whole multitude of eager would-be followers. Self-renunciation, pushed, if necessary, to the extremest issues, is with Jesus the one indispensable condition of discipleship. He asks for nothing less than the heart, and that cannot be given by halves.
The Pulpit commentary also says:
If any man come to me, and hate not his father, and mother, and wife, and children, and brethren, and sisters, yea, and his own life also, he cannot be my disciple. The Lord's teaching throughout, in parable and in direct saying, pressed home to his followers that no home love, no earthly affection, must ever come into competition with the love of God. If home and his cause came ever into collision, home and all belonging to it must gently be put aside, and everything must be sacrificed to the cause.
The word disciple is certainly a favorite of Jesus but was used extensively by Luke in Acts 6:1, 2, 7, 9:1, 10, 25, 26, 38, 11:29, 13:52, 14:20, 22, 28, 15:10, 16:1, 18:23, 27, 19:1, 9, 30, 20:1, 30, 21:4, 16.
A “disciple” is a student, i.e., one who learns from and is taught by a teacher.1 The English word “disciple” is a loanword from Latin discipulus.
According to Oxford English Dictionary on “disciple”:
Etymology: Originally (in Old English) < (i) classical Latin discipulus
Lewis & Short on the Latin word discipulus:
The Lord Jesus Christ was a teacher. Note the following:
Matt. 22:16:
16 And they sent to Him their disciples with the Herodians, saying, “Teacher, we know that You are true, and teach the way of God in truth; nor do You care about anyone, for You do not regard the person of men. NKJV, ©1982
Matt. 5:1–2:
1 And seeing the multitudes, He went up on a mountain, and when He was seated His disciples came to Him. 2 Then He opened His mouth and taught them, saying: NKJV, ©1982
He taught his disciples (students), and in turn, he commanded them to go and teach the nations.2 In Acts of the Apostles, and the later books, the apostles and other disciples were fulfilling his commandment to do so, hence “the number of disciples multiplied.”3 Although the apostle Paul makes no explicit mention of the word μαθητής (“disciple”) in his writings, the fact that he refers to himself as a “teacher of Gentiles” (διδάσκαλος ἐθνῶν)4 implies that he, too, was making disciples by teaching them “the words of our Lord Jesus Christ and the doctrine which is according to godliness.”5
1 Greek διδάσκαλος; Latin magister
2 Matt. 28:19
3 Acts 6:1, 6:7
4 1 Tim. 2:7; 2 Tim. 1:11
5 1 Tim. 6:3
Lewis, Charlton T.; Short, Charles. Harper’s Latin Dictionary: A New Latin Dictionary Founded on the Translation of Freund’s Latin-German Lexicon. New York: Harper & Brothers, 1884.
As the other answers here note, a disciple μαθητής (mathetes) is a student who studies under a teacher. These were common in Greco-Roman society. The Plotinus and Plato had numerous disciples who studied under them.
Just as with modern day students, once you graduate and are no longer a student, the term is no longer appropriate unless in the past tense (Eg, Jayant Narlikar was a student of Steven Hawking, but is no longer. Similarly, Aristotle was a disciple of Plato until he started teaching on his own.)
By virtue of the fact that the Gospels mostly record the life and teachings of Jesus, there is not much opportunity for others to refer to the Disciples/Apostles as Disciples - and this then is the term mostly used by Matthew, Mark, Luke and John.
With the death of Jesus however, they could no longer study from the the rabbi Jesus, and therefore the term was no longer appropriate. A new term is needed, and in Acts we are told of the day of Pentecost in which the Apostles are sent out to preach the Gospel to all nations.
The term Apostle ἀπόστολος (apóstolos), literally means "one who is sent off" and so from the day of pentacost forward, this was a more appropriate term for Jesus' 12 apostles - they were the 12 who were sent off by Jesus.
As the Epistles and Revelation (the remaining texts of the New Testament) mostly record and concern times after the day of Pentacost, they understandably use the term "Apostle" instead of "Disciple" as this is the appropriate term for the time period that these writings record.
