The UNION of Brest (1595–1596) aimed to heal the lack of canonical unity between the Churches. In the spirit of the 1439 Florentine Union, the Orthodox Church of Kievan Metropolia (today’s Ukraine and Belarus) sought to rekindle ecclesial union with the Roman Apostolic See. Prominent Roman theologians and curialists made theological, canonical, disciplinary, and liturgical arguments why they should be forced to conform to the prevailing Roman Rite. Instead, Clement VIII achieved an authentic, enduring unity by confirming their ancient customs and particularities.
Even after the Union, the bishops-delegates were interrogated by curial cardinals as to why they were not wearing the ‘proper’ vestments. Unity was achieved in diversity, although not all accepted union and “Uniates” were often treated a second-class Catholics.
When Eastern Catholic migrants came to the Americas and western Europe, similar arguments were made, that multiple Rites an Disciplines within the same territory would harm the unity of the Church. Local Roman bishops cited the newcomers’ aversion to the majority Rite as proof of the inauthenticity of their Catholicism. They were accused of disobedience, divisiveness, and having schismatic proclivities. One curial cardinal even cited the Fourth Lateran Council.