 Because Catholic dogma is a part of divine revelation, the saving truths of Christ are immutable.But what truths are dogmas has needed to be clarified by church councils, and the much more numerous doctrines have yielded to varied and increased understanding based on solid study of the Biblical roots and of the history of the topic.For this the work of theologians is indispensable, since the charism of the bishops is not to receive revelations but to determine what is Catholic teaching, the more so in doctrines that are more central to the faith and dogmatically taught.