Since the various Christian traditions are not yet in full, visible and Eucharistic communion with each other, it is preferable and more considerate not to conduct a joint inter-church service in the context of a Mass. Nevertheless,
1. With a diverse congregation representing differing Christian communities, it is important to use the richness of hymns, prayers and forms of liturgy from various Christian traditions. (The Search for Christian Unity IV B)
2. Do not use prayers, vocabulary, signs, etc. that would be unapproachable or offensive to other traditions but find riches from within the Catholic tradition and others which can make the service reflect what Christians have in common
3. Use an already existing “liturgy” or “liturgical order” when Christians come together in prayer. The liturgical order of the host congregation should be followed “according to the books and customs of a particular Church or Community, presided over by a minister of delegate from that tradition.” (The Search for Christian Unity IV B).
The non-sacramental liturgy of a particular tradition will often be preferred to a specially constructed unity service (IV B). Ecumenical prayer services are not an opportunity to make things up as one goes along, or to aim for the “lowest common denominator ecumenism” by watering down the order of worship: rather than making the service feel inclusive by making it neutral, it risks including no one. Great care is needed when preparing ecumenical prayer opportunities. When it is prepared well, it has a lasting effect on the participants.
4. Make the celebration as inclusive as possible by showing sensitivity to all Christian traditions, as well as race, gender and those with learning difficulties or physical disability.
5. Begin as soon as possible to look for a dynamic and inspiring preacher.
6. In unity services using the Catholic tradition (such as Evening Prayer), “other ministers may have place and liturgical courtesies proper to their rank, and Catholic ministers may accept a similar invitation in the service of other tradition” (Search for Christian Unity IV B). Leaders and participants in ecumenical worship may wish to express outwardly the principle of ‘unity-in-diversity’ by using the form of dress according to their tradition. This should be agreed beforehand in discussion with the planning group.
7. Music should reflect the different Christian traditions present, as well as offering an opportunity to enter into the cultural and liturgical tradition of the host congregation in which the service is rooted.
8. At such an important event as a Unity Service, all music and liturgical actions or ceremonies involving participants from different congregations should be carefully rehearsed beforehand. This should be carefully discussed and arranged well in advance with the clergy, servers, readers, directors of music, organists, musicians and singers on whom you will rely on the day.
9. In each service include ministers, readers and musicians from the participating congregations. Make sure the voice of more than one tradition is heard during the prayers and reflections, as well as the readings from Scripture.
10. Pray for the ministers, leaders and members of the Christian congregations in the area, including a petition for prayer to fulfil the prayer of Jesus “that all may be one” (St John’s Gospel, chapter 17).
11. Liturgical colours or other symbols (bells, flowers, incense, water, icons, etc.) should be used with appropriate explanation in a complete, printed Order of Service as a way of further sharing, catechesis and hospitality.
12. There should be no surprises at an ecumenical occasion. The planning group should have prepared for all eventualities. Worshippers should be able to follow all that is happening in a properly produced Order of Service.
Note: Celebrating the Eucharist in the Catholic Church and the Celebrations of other Christian Traditions