I am intrigued–not to mentioned mostly convinced–by the argument that present-day divisions of the church are, in fact, sin. A more complete explanation of this, as well as some direction for the future of ecumenism in the church, can be found in the
Princeton Proposal for Christian Unity.
Another good place to begin if you are interested in ecumenism is with the World Council of Churches’ Baptism, Eucharist, Ministry document.