Unity has its foundation in the oneness of God. There is one God. Therefore all of reality belongs together. All of reality is to be at one with God. When that oneness with God is disturbed, the unity of all reality is disturbed. Alienation from God issues in alienation within reality. This understanding of unity which takes God as its starting point is about more than the unity of churches or Christians. It is about all peoples and, more than that, about all of creation. It is truly ecumenical and ecological. It is a vision of unity amid diversity and change; for God has differentiated reality from reality in the evolving, emerging universe. Unity only makes sense in the context of accepting and valuing difference and distinctiveness. Difference becomes destructive division where this is denied and unity, a deceit.
The New Testament writers and Jesus to whom they testify acknowledge a state of sinfulness and alienation, especially among human beings and human communities, as a state of not being at one with God. Jesus gave expression to an alternative vision: the hope of the kingdom of God. He extrapolated from prophetic hopes that looked to a day when God's will would be established in reality. The vision of the kingdom was a vision of unity, of reconciliation. It envisaged people in their differences finding oneness again with God. Jesus taught his disciples to pray, 'Your kingdom come!' and so to commit themselves to this vision of unity. In specific terms it was about peoples being reconciled, about justice for the oppressed and about the powerful being put in their place; it was about including the excluded, the estranged, outcast, crippled, powerless, women, children, slaves.
In time Jesus himself became the focus of unity; he had claimed that the vision of unity was already emerging into reality during his ministry. His inclusiveness, especially in table fellowship, became a foretaste of what was to come in the kingdom. The eucharist, which emerged from such table fellowship, originates in such meals and so represents a commitment to the vision of universal unity. The events of Easter convinced the disciples both that God was indeed the one whom Jesus served and that Jesus himself had been joined to God's reality in such a way that the Christian community could affirm that to be one with Christ was to be one with God. In some streams of Christianity, for instance in Paul, the risen Jesus, the body or being of Christ, becomes like the realm of God's being, God's Spirit, so that now they could speak of unity in Christ, in the body of Christ, in the Spirit. It is still the same unity which affirms diversity and understands alienation as sin.
The shift from basing unity in the oneness of God to basing it, by extension, in the one Lord Jesus Christ, created tension, especially among Jews, between those who accorded Jesus this central role, together with the growing numbers of non Jews who joined them, and those who did not. Passion for the hope of universal unity, when identified with Jesus in this way, became the cause of disunity as Christians asserted the uniqueness of Jesus and his radical inclusiveness.
As radically inclusive Christian Jews encountered non Jews, a series of crises rocked the early Christian communities. The issues centred around the unity of the Bible and its demands. Some believers argued that the biblical commands should be followed without exception as God's commands, thus preserving the unity of Scripture. Some did so, while acknowledging that some things were certainly much more important than others, a stance which Jesus had espoused; but then he had not been facing the new situation with non Jews. Some began to allow exceptions (on circumcision, for instance). Others, like Paul, proposed abandoning almost all except the central ethical commands of scripture. Christianity very early fell into division over unity, namely the unity of scripture; those who argued from the vision of Jesus proposed a universal approach which was prepared to abandon much of what the Bible commanded. The divisions were raging at the time that Paul wrote, who sought meetings with apostles and argued with critics, but refused to compromise for the sake of unity among the churches, because he held fast to his conviction about Jesus' vision of unity.
Some of these positions remained alive a generation later, at the time when the gospels were written, though the heat had gone out of the conflict. Mark continues Paul's radical line. Matthew still argues for keeping all commands. Luke forges a history of the earlier period which blurs much of the division. He has Paul and Peter and James at one and both Jews and Gentiles in total conformity with scripture. He can do this by portraying much of biblical Law as a gift of customs to the Jews. John has transformed the old into a source of imagery and metaphor for the new and little more. He has Jesus turn his back on Judaism and call for unity only with himself and with God as his Father and so his Jesus prays for the disciples that they may be one. The vision of unity in John is primarily limited to the Christian community and is doubtless emphasised because John's community threatened to fall apart on precisely how to understand the nature of Jesus who is the basis of unity. The split had occurred by the time of 1 John, shortly after.
In Paul's churches in this later period the vision of universal unity remerges in Colossians which speaks of the reconciliation of the whole of reality in all its fullness taking place as it is incorporated into Christ's body. Here the Christian community, the church, sees itself as the first sign of progress towards this hope, a sign of unity. Ephesians then employs the same image to celebrate that such incorporation had brought together Jews and Gentiles as one (Christian Jews and Gentiles, of course). Unlike some of the other models, like the oft quoted Johannine one, this image of the body, which will be filled with all the fullness of reality that God has created and so restore unity and reconcile all things, comes close to being a restatement of Jesus' hope of the kingdom, at least in its universal perspective. It has at times led the church to think over highly of itself, especially when it saw itself as the kingdom in the present instead of as the community in which God's reign is at least being celebrated and partly realised, but far from being perfectly realised.
If it is to remain close to Jesus' vision, the vision of unity needs to be taken so seriously that it works itself into present reality in all its aspects. It cannot be truncated to inter-church unity, but must retain its character of being a vision of justice and peace for all peoples and for the whole creation. Inter-church unity only makes sense within this broader context; otherwise it looks all too much like a ghetto strategy for survival. The vision of unity needs to take seriously the divisions within Christianity and from Judaism and assess them within this broader perspective. This perspective needs to drive concern about church unity and may indeed lead to conflict at times rather than unity. Seeing God (and, derivatively, the kingdom vision, and then, Jesus) as the basis for unity freed many believers to avoid attributing absolute status to the Bible and to cultural tradition. Probably cross cultural encounter also played a significant role in relation to the latter. Where churches comprehend the strictly theological basis for unity, they may be able to see their own religious traditions in such a perspective, even if they still insist their particular culture was God given.
This becomes an issue both in the diverse forms of Christianity which have emerged in the last millennium and in the dominant forms which evolved in the first centuries of the Christian era. For then, pragmatic solutions emerged in response to mission and survival which forged the identity of Christianity for the future: in canonising the scripture, establishing sacramental patterns, instituting patterns of ministry, formulating creeds. These became points of demarcation from others and the basis for unity of those who remained in control. These have been so strong that it is not possible, and many would say, not appropriate, to appeal to the biblical basis of unity beyond them. Yet despite this fact, commitment to unity must include the lively, open and honest, juxtaposition of streams and statements of the tradition, including biblical tradition, and the ongoing flexibility to enable the vision of the kingdom as espoused by Jesus not to be lost. The quest for unity is one of the ways of losing that vision where harmony compromises justice and love; but, informed by the theology of compassion enunciated in Jesus' vision of the kingdom and lived in his life, the quest for unity gives expression to heart of the gospel.