Disciples is the term used in the four gospels and Acts, Saints is the term used in the letters and Overcomers is the term used in Revelation (chapters 2 & 3). And I believe they all refer to the same thing – they mean Christians who are loving the Lord their God with all their hearts and all their minds and all their souls and all their strength and their neighbours as themselves (Matthew 22:37-40).
Disciples take up their cross daily and lose their lives so they may save them (Luke 14:26-27). Saints live holy lives dedicated to their God and the fellowship of other saints. Overcomers keep on coming over and over again to the Lord no matter what. They all by faith and patient endurance take hold of the promises God has in store for those who love Him (Hebrews 6:11-12).
And the New Testament is written for them not for anyone else really.
Unless you are born again you cannot be a disciple and you cannot see the things they see (John 3:3 & 5). However being born again is not enough, you must also walk daily with Jesus if you want to gain the promises made to overcomers (Rev. 2:7, 11, 17, 26-28; 3:5, 12, 21) .