The advice of Pope Saint Gregory the Great (590-604) to Augustine of Canterbury, as a model of communion for the contemporary (postmodern?) ecclesial scene:
Agustine’s Second Question: Even though the faith is one, are there varying customs in the churches? And is there one form of Mass in the Holy Roman Church and another in Gaulish churches?
Pope Gregory answered: My brother, you know the customs of the Roman Church in which, of course, you were brought up. But it is my wish that if you have found any customs in the Roman or the Gaulish church or any other church which may be more pleasing to Almighty God, you should make a careful selection of them and sedulously teach the Church of the English, which is still new in the faith, what you have been able to gather from other churches. For things are not to be loved for the sake of a place, but places are to be loved for the sake of their good things. Therefore choose from every individual Church whatever things are devout, religious, and right. And when you have collected these as it were into one bundle, see that the minds of the English grow accustomed to it.
From The Venerable Bede, Ecclesiastical History of the English People, as quoted in Frederick M. Bliss, Catholic and Ecumenical: History and Hope – Why the Catholic Church is Ecumenical and What She is Doing About It, p9.