They were discipled through Christ's crucifixion to annul their human life for them to live the divine life (Gal. 2:20).
They were also discipled through Christ's resurrection to know Him as God's firstborn Son (Rom. 1:4; Acts 13:33; Rom. 8:29). As the only begotten Son of God, Christ had only the divine life and nature. He had nothing human. But as the firstborn Son of God, He is both divine and human. Christ had the human life and nature, but He lived the divine life and nature through the denying of His human life and nature. This was His divine and mystical living to disciple all His followers for three and a half years.
They were also discipled to know Christ as the life-giving Spirit (1 Cor. 15:45).
Christ's resurrection was for the producing of the many sons of God as His multiplication and increase (Heb. 2:10; John 12:24).
If we open to the Spirit within us as we prayerfully consider this fellowship, we will be discipled. Only the discipled ones are the constituents of the vital groups. They have been discipled to be vital. A disciple is one who lives the divine life in his human life. The vitality of the ministry is due to a person's living the divine life out of his human life. Then what he utters is divine out of a crucified human life. We need to deny our human life for the releasing of something divine. This is the main factor of our being vital.
Eventually, we are the witnesses of Christ. In Acts 1:8 the Lord told the disciples, "You shall be My witnesses both in Jerusalem and in all Judea and Samaria and unto the uttermost part of the earth." A witness is one who has seen something. After Paul was saved on the road to Damascus, the Lord appointed Paul to be His witness (Acts 26:16).
The disciples witnessed that Christ had resurrected (Acts 1:22; 3:15; 10:39-41; 13:31). If we witness that Christ has resurrected, we must live a resurrected life.
The resurrected Christ was anointed by God to carry out His commission (Acts 10:38-39).
The resurrected Christ was made by God the Lord of the whole earth and the Christ, the Messiah, for carrying out God's economy (Acts 2:32-36). He was also made the Leader and Savior (Acts 5:30-32). He is the Ruler of the kings of the earth (Rev. 1:5) and the One who controls the whole earth to arrange the situation so that His chosen ones may believe into Him as their Savior to be saved. Also in His resurrection He was made by God the Judge of the living and the dead (Acts 10:42). He will judge the living on His throne of glory (Matt. 25:31-46), and He will judge the dead on the great white throne (Rev. 20:11-15).
The crucial point of the witnesses of Christ is that they live Christ (Acts 22:15; Phil. 1:21a; 2 Cor. 13:3) in His resurrection and through His death (Phil. 3:10). They do not merely preach or speak about Christ, but they live a life which witnesses Christ.
The constituents of the vital groups are the believers in Christ, the disciples of Christ, and the witnesses of Christ. All of the full-time trainees need to realize that they are being discipled by Christ's human living, by His all-inclusive death, and by His life-dispensing resurrection. After the training they should go out not just to teach, preach, and propagate but to witness. By the Lord's mercy, I have been discipled for about seventy years, and I am still under the Lord's discipling today.