Christianity has historically taken correct doctrine very seriously. The early fathers and church councils carefully distinguished between "orthodoxy" from "heresy" in an effort to preserve what they saw as the true Christian message. Throughout the Middle Ages, the decisions of the ecumenical councils and the doctrine of apostolic succession ensured that correct belief was safeguarded. However, this did not stop great minds like Thomas Aquinas from exploring and even questioning all aspects of Christian theology within the bounds of orthodoxy.
During the Protestant Reformation in the 16th century, attention turned once again to preserving the original message of Christianity. Reformers called for the stripping away of the many superfluous and even erroneous doctrines that had developed over the centuries and demanded that theology be based on the Bible alone. The importance of right belief was brought even more to the forefront with the reformers' emphasis on true faith as the only requirement for salvation. Almost all of the denominational divisions that have arisen since the Reformation center around matters of doctrine, not practice.
Given the great historical attention that has been devoted to it, the 2,000 years' worth of available writing on its many subjects, and its sometimes complex philosophical arguments, Christian doctrine can be an intimidating subject for the beginner. The following articles therefore attempt to summarize the general consensus of Christian beliefs on everything from God to the afterlife, with historical development and denominational differences taken into account as much as possible.