First, I will define the minimum of truth that defines a Christian.
Now, brothers and sisters, I want to remind you of the gospel I preached to you, which you received and on which you have taken your stand. By this gospel you are saved, if you hold firmly to the word I preached to you. Otherwise, you have believed in vain. For what I received I passed on to you as of first importance: that Christ died for our sins according to the Scriptures, that he was buried, that he was raised on the third day according to the Scriptures, and that he appeared to Cephas, and then to the Twelve. (1 Cor. 15:1-5)Second, I will define the response to this truth. There are several works that are used in this response.
Yet to all who did receive him, to those who believed in his name, he gave the right to become children of God. (John 1:12)These nine verbs are not synonyms, but they describe a synonymous action in that they all result in eternal life. The Lord is the object of each verb.
For God so loved the world that he gave his one and only Son, that whoever believes in him shall not perish but have eternal life. (John 3:16)
Very truly I tell you, whoever hears my word and believes him who sent me has eternal life and will not be judged but has crossed over from death to life. (John 5:24)
Come to me, all you who are weary and burdened, and I will give you rest. (Matt. 11:28)
But Peter and John replied, "Which is right in God’s eyes: to listen to you, or to him? You be the judges!” (Acts 4:19)
If you declare with your mouth, "Jesus is Lord," and believe in your heart that God raised him from the dead, you will be saved. For it is with your heart that you believe and are justified, and it is with your mouth that you profess your faith and are saved…for, "Everyone who calls on the name of the Lord will be saved. (Rom. 10:9-10, 13)
…open their eyes and turn them from darkness to light, and from the power of Satan to God, so that they may receive forgiveness of sins and a place among those who are sanctified by faith in me. (Acts 26:18)
Third, there are descriptions of this new life in Galatians 5:22-24: “But the fruit of the Spirit is love, joy, peace, forbearance, kindness, goodness, faithfulness, gentleness and self-control. Against such things there is no law. Those who belong to Christ Jesus have crucified the flesh with its passions and desires.”
“For we were all baptized by one Spirit so as to form one body—whether Jews or Gentiles, slave or free—and we were all given the one Spirit to drink” (1 Cor. 12:13). Everyone baptized by the Spirit is part of the one body of Jesus Christ.
“Make every effort to keep the unity of the Spirit through the bond of peace. There is one body and one Spirit, just as you were called to one hope when you were called” (Eph. 4:3-4). We are to be eager to maintain the oneness we had when we entered the body.
There seem to be three biblical reasons to break fellowship with other Christians.
1. Apostasy: Those who no longer believe the gospel.There are several ways of being “closed.” Closed means excluding from, or not participating in, fellowship with those Christians who do not fit certain standards. These standards are in addition to the ones described above.
2. Unrepentant immorality: “What business is it of mine to judge those outside the church? Are you not to judge those inside? God will judge those outside. ‘Expel the wicked person from among you” (1 Cor. 5:12-13).
3. A divisive person: “But avoid foolish controversies and genealogies and arguments and quarrels about the law, because these are unprofitable and useless. Warn a divisive person once, and then warn them a second time. After that, have nothing to do with them. You may be sure that such people are warped and sinful; they are self-condemned” (Titus 3:9-11). “I urge you, brothers and sisters, to watch out for those who cause divisions and put obstacles in your way that are contrary to the teaching you have learned. Keep away from them” (Rom. 16:17).
“Closed” Christians extend the reasons for breaking fellowship beyond these three found in the Bible.