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The first time the word disciple appears in the New Testament is in Matthew 5:1.
Matthew 5:1 And seeing the multitudes, he went up into a mountain: and when he was set, his disciples came unto him:
Using Strong’s Concordance and a Greek Lexicon:
Disciples - Strong’s number 3101 – Greek ‘mathetes’ - noun (from 3129 ‘manthano’ to learn). Meaning - a learner or pupil.
From this we see that ‘disciple’ means one who is taught, with the implication that he or she does what they have been taught. Not all continued some turned back.
John 6:66 From that time many of his disciples went back, and walked no more with him.
The disciples who remained faithful, having been taught were to teach others and baptise those who believed.
Matthew 28:19 Go ye therefore, and teach all nations, baptizing them in the name of the Father, and of the Son, and of the Holy Spirit:
Mark 16:15 And he said unto them, Go ye into all the world, and preach the gospel to every creature. 16 He that believeth and is baptized shall be saved; but he that believeth not shall be damned.
This they did.
Acts 5:42 And daily in the temple, and in every house, they ceased not to teach and preach Jesus Christ.
Those that heard and believed, responded by being baptised.
Acts 8:12 But when they believed Philip preaching the things concerning the kingdom of God, and the name of Jesus Christ, they were baptized, both men and women.
The doctrine was fixed.
1 Timothy 1:3 As I besought thee to abide still at Ephesus, when I went into Macedonia, that thou mightest charge some that they teach no other doctrine,
The gospel was fixed.
Galatians 1:8 But though we, or an angel from heaven, preach any other gospel unto you than that which we have preached unto you, let him be accursed.
We are called whenever we hear or read the word of God. Do not be deceived by those who claim a supernatural individual calling.
Faith or belief comes from one place only.
Romans 10:17 So then faith cometh by hearing, and hearing by the word of God.
What Jesus taught is written down in the New Testament.
Acts 1:1 The former treatise have I made, O Theophilus, of all that Jesus began both to do and teach,
John 20:31 But these are written, that ye might believe that Jesus is the Christ, the Son of God; and that believing ye might have life through his name.
2 Timothy 3:15... from a child thou hast known the holy scriptures, which are able to make thee wise unto salvation through faith which is in Christ Jesus. 16 All scripture is given by inspiration of God, and is profitable for doctrine, for reproof, for correction, for instruction in righteousness: 17 That the man of God may be perfect, throughly furnished unto all good works.
If we allow ourselves to be taught by the scripture and believe the gospel concerning the kingdom of God and the name of Jesus Christ and are baptised, then we become disciples. As disciples we are to live by Christ’s commandments.
John 8:31 Then said Jesus to those Jews which believed on him, If ye continue in my word, then are ye my disciples indeed;
John 15:8 Herein is my Father glorified, that ye bear much fruit; so shall ye be my disciples.
The reward for faithful discipleship is eternal life in the kingdom of God.
I hope this helps.