D. A. Carson, The Farewell Discourse and Final Prayer of Jesus: An Exposition of John 14–17 (Grand Rapids: Baker, 1980), 201–4:

To some people, the term ecumenism has only good connotations. Utter the word, and they hear harps playing and angels singing; or if harps and angels are deemed too ethereal, at very least a certain fire lights up their eye. To others the same word evokes only images of evil. Ecumenism is intrinsically a doctrine of compromise which emasculates the gospel and wickedly flirts with apostasy and assorted forms of unbelief. The first group tends to cite John 17 in its favor; the second group tends either to ignore John 17 or else to include within the unity only a very small group, while defining the unity in such innocuous terms (e.g., making it entirely a positional unity with no entailment for conduct) that it becomes difficult to see how such unity could ever serve as a witness of anything to the world. What does the text say? [Read more…] about Carson on Ecumenism and John 17