The Church is a community of a message: the message that the God of Israel has raised His Servant Jesus from the dead.
According to Robert Jenson, it is the belief in and proclamation of this message that gives a group of people the authority to call themselves a Christian community. This message is the essence of the Church, uniting Russian Orthodox to American Pentecostal to Irish Catholic. Therefore to be unwilling or unable to confess that "the God of Israel raised His Servant Jesus from the dead" is to exclude oneself from the life of the Church. That is to say, the community that does not confess this is not the same community that began with the apostles.
Does this represent a lowest-common-denominator approach to ecumenism? Some may argue that it does, but since when is there anything "low" about such a stunning confession? To think that the message that the God of Israel raised His Servant Jesus from the dead is insufficient to unite all who believe and proclaim it is perhaps a sign that the message has not really been understood.