Christians must be careful thinkers, especially those who teach other Christians how to think. Very few heresies were the result of self-understood snakes sneaking into the church. Most doctrinal mistakes, of which “heresy” is only the most serious category, come from well meaning people intent on safeguarding an important element of the faith.
Arianism and Docetism were two of the church’s first and deadliest heresies. And yet, both were attempts to preserve the truth. Arianism wanted to defend the majesty of God. So Arius stopped short of affirming the full deity of Christ. Surely the glory of God would be compromised if we make the human Son equal with the divine Father. Docetists saw the problem moving in the opposite direction. They too wanted to defend the perfection of God. So they refused to affirm the full humanity of Christ. Surely the Son must only appear to be human. How else can we protect the full splendor of this divine Savior?
Both sides were both trying, at least in part, to protect the truth, but their human logic and philosophical assumptions prevented them from seeing the whole truth. They defended what was right by devaluing what wasn’t wrong. This doesn’t mean the right answer is always the mythical third way or some combination of all the options. But it does mean we ought to avoid the mistake of making the Bible fit our grid instead of allowing for complementary scriptural ideas to work side by side.
Almost every doctrinal error starts with the desire to affirm or to protect some important doctrine. But without careful thinking and delicate nuances, working hard to avoid one mistake will simply lead us to another. Maybe even worse.