Page "Unitatis Redintegratio" Paragraph 9

The document acknowledges that there are serious problems facing prospects of reunion with Reformation communities that make no attempt to claim apostolic succession such as the Anglican communion does.

Ecclesial communities that adhere to calvinism are a particular case because they often have important doctrinal differences on key issues such as ecclesiology, liturgy and mariology.

Other communities have insoluble doctrinal differences with Catholic Christianity because their theology of the Holy Trinity is manifestly incompatible with the doctrine of the council of Nicea in the early Church.

That these serious problems are a barrier to salvation is clarified in the 2004 Vatican document, " The Decree on Ecumenism, Read Anew after Forty Years ".