Here are just a few implications of things that I've been waffling about so far on the nature of Christian unity. They're not designed to be a complete blueprint for all future activity expressive of Christian unity, but I do think they're things that people ought to take on board.
Future ecumenical activity should have a strong confessional basis
Since Christian unity is based on truth, attempts to display that unity must also be based on the truth. If big ecumenical events are planned, they should have at their heart a statement of the gospel around which we are uniting. This will doubtless exclude some people who have hitherto been involved in events, although it may also encourage some who have not been involved wholeheartedly to come onboard. However, even if this course of action seemed pragmatically undesirable, we should take it because it allows us to draw the lines in the same place as the New Testament.
Unity need not flow from church leaders or structures
An informal Bible study group consisting of people from different churches is as much a display of the visible unity that the New Testament calls for as a meeting of church leaders, or an event jointly organised by different churches. In many ways this sort of grass-roots unity is a better expression of Christian unity than an organised event, because it flows more directly from the sense of a shared experience of the Spirit and a shared commitment to the truth.
Christian unity will only be made visible through relationships
At one level this simply flows from the nature of the unity that we see in God the Trinity. At a more pragmatic level, it is necessitated by the need to assess the visible evidence of spiritual unity that I have argued for. Only in the context of a relationship can there be the realisation that we share the same experience of the Spirit and the same faith. This is as much true for Christian churches and organisations as it is for individuals.
No individual, church or organisation should be asked to commit to a programme or event in which they have no control over who else is invited to join
This follows from the previous point. It is not reasonable to ask Christians to unite with others when they have had no chance to ascertain whether they show evidence of spiritual unity.
To decline visible unity with someone is not necessarily to impugn their salvation
There are many valid reasons why a Christian, Church or organisation may decline to unite visibly with another group or individual. The most obvious would be that they simply do not know whether they share the same faith and the one Spirit. However, no person or group’s choice to decline unity in any given situation should be understood to mean that they do not believe another person or group to be spiritually united to Christ. At worst, they may claim that the other person or group does not seem to share the faith and experience of the Spirit which they are looking for as evidence of their spiritual unity. However, charity demands that we not assume that persons or groups declining unity are making even this limited judgement unless they specifically say so.
Within those limits, I think that we should be seeking to maintain the unity God has given us - putting real energy into doing so, with enthusiasm. And I think we should be making that unity visible - whether through big events, joint ventures, or just co-operation locally - so that the world can see that we are Christ's disciples.