Today’s Christianity is not, without a doubt, a collection of the unvarnished teachings of Jesus to the apostles. Part of the reason for this has to do with the transmission of his words, but part of it has to do with the dynamic between Christian teachings and heresies.
To understand what happened one need only grasp a few things about two terms and one phrase.
The first of these is orthodoxy (from the Greek meaning “true teaching”). This is what Christian leaders, such as the apostles, taught and understood to be the teaching of Jesus. Even so, inevitably difficulties arose in passing these on or answering questions from after the teachings were given and received.
The opposite of teaching, or a choice to depart from them, is called heterodoxy or heresy, respectively. The funny thing about heresy is that it usually involves an aspect of orthodoxy. The error, as heresy has been historically been called, consists in exaggerating the significance of some small part of teaching.
For example, sometime in the sixth century some Christians opposed the use of icons or images, arguing that this is against the commandment forbidding graven images (“You shall not make for yourself an idol” Exodus 20:4). The iconoclasts, or icon destroyers, went about smashing religious images until Christians came to recognize that so long as one did not actually worship the images, but rather used them to recall what they evoked, the spirit of the commandment was fulfilled.
In the heresy of iconoclasm, the truth of the teaching against idols was exaggerated in importance, to the point of justifying violence and disrespect to what others valued. The teaching had only meant to stop believers from imagining that inanimate things could have special and divine powers—not from painting or carving images that would remind them of other true teachings.
Finally, there is the phrase “development of doctrine,” which explains how Christians dealt with questions, heresies and other problems not envisioned by the discourses of Jesus in the gospels or apostolic interpretation. To some, this means that the apostles and their successors, the bishops, had to make things up, possibly perverting the original.
However, from apostolic times, great effort was made not to add to the faith, but rather to cut off what is not in consonance with received teaching. The latter approach is called the via negativa: the road of negation.
The apostles and bishops felt they could authoritatively say, “this goes beyond or distorts what Jesus taught.” They did not feel they could add new teachings.
When considering such questions, keep in mind that teachings concern essentials, such as the existence of God, that Jesus is the Messiah or God forbids murder. Lesser matters, such as the various rules of rituals and other practices are disciplines, good for you perhaps (or not), but not essential.