11 The way and method in which the Catholic faith is expressed should never become an obstacle to dialogue with our brethren. It is, of course, essential that the doctrine should be clearly presented in its entirety. Nothing is so foreign to the spirit of ecumenism as a false irenicism, in which the purity of Catholic doctrine suffers loss and its genuine and certain meaning is clouded. At the same time, the Catholic faith must be explained more profoundly and precisely, in such a way and in such terms as our separated brethren can also really understand. Moreover, in ecumenical dialogue, Catholic theologians standing fast by the teaching of the Church and investigating the divine mysteries with the separated brethren must proceed with love for the truth, with charity, and with humility. When comparing doctrines with one another, they should remember that in Catholic doctrine there exists a "hierarchy" of truths, since they vary in their relation to the fundamental Christian faith. Thus the way will be opened by which through fraternal rivalry all will be stirred to a deeper understanding and a clearer presentation of the unfathomable riches of Christ.
Source: Unitatis Redintegratio (Vatican.va)