Oikos

"We have inherited a big house, a great "world house"[oikoumene] in which we have to live together - black and white, Easterners and Westerners, Gentiles and Jews, Catholics and Protestants, Moslem and Hindu, a family unduly separated in ideas, culture, and interests who, because we can never again live without each other, must learn, somehow, in this one big world, to live with each other.
This means that more and more our loyalties must become ecumenical [oikoumene] rather than sectional. We must now give an overriding loyalty to mankind as a whole in order to preserve the best in our individual societies.
This call for a worldwide fellowship that lifts neighborly concern beyond one's tribe, race, class, and nation is in reality a call for an all-embracing and unconditional love for all men."
- Dr. Martin Luther King Jr - Nobel Peace Prize Lecture - Dec. 11, 1964

SOME ECUMENICAL ETYMOLOGY The root of the word "ecumenical" is oikos, a Greek word in the Bible meaning "house." We find oikos in words like "economy" and "ecology." Therefore "ecumenical" has to do with the "household" of God - and oikoumene is a "world house" (see MLK above). I interpret various scriptures about the God's plan/telos/end as being that All (panta) people are to realize they are brothers and sisters in God's household. More
Another Greek word tells us how to participate in God's goal -- that is, to turn strangers into com-panions around the table of dialogue. Xenos means "stranger," as in xenophobia "fear of strangers (we see that as an overriding social/political pathology). Paradoxically, the Greek word for "hospitality" is xenia which means a "stranger turned into a guest."
While the word "ecumenical" has traditionally described the movement for unity within the Christian house, as against the words "interreligious" or "interfaith" meaning relationships to religions outside Christianity, I believe "ecumenical" can be correctly used to in relation to other faiths. (Again MLK) As such it connotes, not a movement to co-opt into unity, but a recognition of the Holy Spirit working amid the whole household toward the telos/end of a world family reconciled in a just peace. Interfaithing is a imperative verb for this whole household. You can draw some ecumenical views from Ephesians 1:10; John 17:21; Acts 2; Acts 9:10f; Acts 15:12f; Luke 4:24f; Mark 7:24-36.