12 Now if these only aimed at adapting ecclesiastical teaching and methods to modern conditions and requirements, through the introduction of some new explanations, there would be scarcely any reason for alarm. But some through enthusiasm for an imprudent "eirenism" seem to consider as an obstacle to the restoration of fraternal union, things founded on the laws and principles given by Christ and likewise on institutions founded by Him, or which are the defense and support of the integrity of the faith, and the removal of which would bring about the union of all, but only to their destruction.
Source: Humani Generis (Vatican.va)