There is no such thing as another Church or a Sister Church or whatever you wish to designate with a predicate 'Church' indicating anything other than there being ONE TRUE CHURCH
[Florence, Trent etc etc etc Mirari Vos, Satis Cognitum etc etc etc]
We are ABSOLUTELY FORBIDDEN from engaging in joint worship services.
[Pius XI Mortalium Animos]
We are also forbidden from praying together or praying with - but permitted to pray among and alongside [the Assisi 3 criteria]
ANY Prayer for Christian Unity [in congruency with John 17] demands that every baptised repents, converts and returns to the One, Holy Catholic and Apostolic Church - that is the ONLY permissible and recognisable Unity.
Oecumenical literally means 'Household issues" ie what solely relates to the Catholic Church - and Oecumenism therefore means OUR Mission to evangelise and convert baptised non-Catholics [ie those who are absolutely our responsibility being baptised though schismatic] and guarantee their return to the fold...
It's OUR REMIT - nobody else's
It has absolutely nothing to do with any other community or sect or cult
And we are not there to dialogue, or compromise, or negotiate or 'faith-share' or 'experience-share' - we are there to convert!
That is the only message of sincerity and authenticity - the real Truth in Love .
..and the only way we can possibly engage in any activity with other religions is to make it absolutely clear to them that although we love them and respect them - we do not give their heresy, heterodoxy, heteropraxy and untruths any credence or respect whatsoever - and absolutely seek to inform, instruct, evangelise and convert anyone and everyone.
Hasn't it possibly occurred to you that all these 'interfaith service' activities ultimately proved fruitless and hollow was because they were grounded in insincerity and ultimately deceit?
Anglican protean 1000-masked relativism might hoodwink the many UNTIL the unacceptable is accepted [or have you been at an oecumenical service where the baptists blow a gasket because of reference to Our Lady as the Mother of God and Methodists storm out when a vicar dares to commence a prayer for the dead of the community?!! Ever been at an 'interfaith' Justice & Peace group where a stand up fight commences because the Catholics say abortion, euthanasia and population control are evil yet individual christian groups think one or more of those ethical issues are acceptable? ]
Now yes OF COURSE food banks, drop in centres, counselling resources, cafes, soup kitchens, homeless shelters etc will thrive and survive and be successful amongst the religious groups - they're natural law obligations on every human being to their neighbour irrespective of their credal position...
...and yes they might indirectly lead to interaction between those of differing faiths and none WHILST they are engaged in a mutual activity.
BUT - what in the name of all sanity has that to do with oecumenism?
Maybe the oecumaniacs with dialogue-fixation and faux interfaith group-hug initiatives need to go back to the drawing board?
...and I say this coming from a family of Catholics, Anglicans, Methodists, Presbyterians, Atheists, Evangelicals, Buddhists and Jews.
...and coming from a town with nearly a century's history of Catholic vs Protestant antagonism which became integrated reconciliation simply by getting on with life, interacting in family and the community and the workplace and recognising 'a man's a man for all that'