When we think about church unity we need to be clear on what the church is. My understanding of the church is a community of sinful people saved by God who strive to continue Christ ‘s mission in the world.
If we see the identity of the church in terms of (1) a community of people in relationship with Christ, (2) as continuing Christ’s mission in the world, and (3) acknowledging that the church’s members are sinners, church unity will enhance the church’s witness in the world. Christian unity is in the spirit just as Jesus and the Father were one in spirit (Jn 17:21). From this unity of the spirit the church can show its unity to the world through its mission. Doctrinal differences have more to do with heritage and academic considerations than a spiritual relationship with Christ.
Physical church unity is only important in as much as it makes for efficient and productive mission. In other words, the existence of many denominational organisations is of no importance provided that it does not make the church ineffective in its mission. Combined church ministries, evangelistic campaigns, social welfare organisations, and missionary organisations are evidence of the essential unity of the church.
All Christians are part of God’s family, family disputes do not change the fact that we all belong to the one church of God. Our relationship is with God and none of us is in Christ’s body by any distinctive of our own. When we look for a distinctive in ourselves as the basis for church unity (as with our salvation) we are detracting from the grace of God. Just as Jesus accepted that the enemy has planted weeds in his field, we will need to accept this too.
The presence of sin in the church is not a reason to become defensive, but a reason to praise God for the salvation of sinners in Christ. This does not mean that we should “continue in sin in order that grace may abound” (Rom 6:1). Sin is the reason behind church splits. It is not just the other party’s sin, but the blind spot that does not recognise that we are just as sinful and in need of God’s grace. There is no “us” and “them” in the church, only us sinners in need of a saviour. Schism is evidence of our sin. Christian unity is evidence of our salvation.