The kingdom life is the God-man life.
In summary, what is covered in Matthew 18:15-22 unveils to us how to take care of a sinning brother in a vital group. You should go and reprove him between you and him alone. If he hears you, you have gained your brother (v. 15). If he does not hear you, take with you one or two more, that by the mouth of two or three witnesses every word may be established (v. 16). If he refuses to hear them, tell it to the church (v. 17a). If he refuses to hear the church also, the vital group should pray by exercising the authority of the church, which is the authority of the kingdom (vv. 17b-18; 16:18-19). Such a situation is dealt with by the vital group in harmony with the Lord in their midst (vv. 19-20) with a forgiving spirit (vv. 21-22). By this way the vital groups live the God-man life as Christ did when He was living on the earth.
The purpose of the vital groups is also to live the church life. Second Timothy 2:22 says, "But flee youthful lusts, and pursue righteousness, faith, love, peace with those who call on the Lord out of a pure heart." This is the way to live the church life by the vital groups.
Paul said in Romans 14:17 that the kingdom of God is not a matter of eating and drinking but of righteousness, peace, and joy in the Holy Spirit. This kingdom life is practiced and realized in the church life.
We must live the kingdom life according to Matthew 5 through 7. Then we can live the church life.
We live the church life by pursuing righteousness. To pursue righteousness is to take care of God's righteous way. Matthew 5:20 says that unless our righteousness surpasses that of the scribes and the Pharisees, we shall by no means enter into the kingdom of the heavens. The kingdom is a matter of righteousness (Rom. 14:17a), and according to the Epistles, this surpassing righteousness is Christ Himself lived out from us (Phil. 3:9). We have to live out Christ as our righteousness.
To pursue faith is to take care of God's faithfulness. Hebrews 11:6 says that without faith it is impossible to be well pleasing to God. Also, when we come to God, we must believe that God is and we are not and that He is a rewarder of those who seek Him diligently. We should pursue faith that links us with God. We must be a person linked with God.