Another reason to study Church History is to combat theological errors or heresies. I all ready wrote about learning from the errors of others, but I was mostly thinking at that time about errors of those who would be considered orthodox or accurate in their theology. We can also, however, learn from those who have been labeled heretics in order to better understand our own theology.
Ever since there has been good or correct theology there has been bad or incorrect theology. Much of it stems from attempting to understand the deep things of an infinite God in our finite minds. We need to attempt to understand God as best we can, realizing that none of those concepts will be understood exhaustively. It is our responsibility to do the best we can at understanding all we can about God.
When discussing the topic of preparing ourselves as Christians to combat bad theology, I use the example of some assertions made by Dan Brown in his book The Da Vinci Code. In this book the main character, Robert Langdon, has a discussion about the Council of Nicaea which was held in AD 325. The assertion is made that Emperor Constantine threw out all parts of the Bible that denied Jesus’ claim of divinity, claiming that the Apostles never believed in Jesus’ deity. They knew he was not God but Constantine was trying to unite the Empire to force the idea of the divinity of Jesus on the people. Langdon was told that Jesus never claimed to be God nor did the disciples think he was God, but Constantine desperately wanted to unite the Roman Empire and he thought keeping the documents that express Jesus deity would help in this unification. The point is stating that Constantine manipulated the choosing of certain books to be put in the Christian Bible in order to further his political agenda. In other words, the Christians did not believe Jesus was God up to this point in time, but Constantine forced them to choose certain books to push his agenda. This WILD assertion was widely accepted by the American people (including Christians) who read The Da Vinci Code as historical fact, when in reality the Council of Nicaea had NOTHING to do with canonization of scripture. My point is had readers of this popular book known their Church History they would not have been deceived by this wild idea.
We need to study Church History in order to combat bad theology we read and listen to in or our contemporary culture. There is nothing new under the sun, and most (if not all) the bad theology that comes up in our day has already been dealt with.
So go out and study Church History, learn to combat bad theology.