Just read in Limited Church: Unlimited Kingdom by Rob Rienow:
The doctrine of the sufficiency of Scripture is a narrow path that leads to pleasing God in all things, but there are deep ditches on both sides. These ditches are the detours to sin and death. On one side is the ditch of rebellion, on the other side the ditch of legalism.
I believe the ditch of rebellion is easier to see. Do you remember the warnings from Deuteronomy and from Jesus not to "take away" any words of the Bible? This is a warning against rebellion... When we deliberately think or act contrary to God's revealed will in the Bible, that is rebellion. When we disregard any portion of Scripture, we have begun sliding down the steep slopes of rebellion.
One of the most surprising things I have learned as I have explored the doctrine of the sufficiency of Scripture is that there are more warnings in the Bible against adding to what God has said compared to the warnings against taking away. For whatever reason, the ditch of rebellion seemed like a big, scary one, with the sharp rocks and wolves waiting at the bottom. The other side, the ditch of legalism, was bad, sure, but certainly not as bad as rebellion... Right? Not according to God.
When we take away from God's Word that is rebellion. When we add to God's Word that is legalism... I am convinced that many churches today are filled with legalism, and they don't even know it!
Simply defined, legalism is creating human rules for righteous living, which are not in the Bible, and judging yourself and others by those human rules...
Legalism is not seeking to follow the Bible in every area of thought and life. Legalism is adding human rules and regulations on top of the Bible...
A legalist is not someone who seeks to rightly obey and apply every word of the Bible to his or her life. A legalist is someone who disobeys the Bible by adding to the Bible human rules and regulations for thought, life, and morality, and proceeds to judge themselves and others by these rules. A legalist is not someone who places divine law above all else. A legalist is someone who places human law above all else...
When legalism infects a church, the results are predictable. Leaders become prideful and divisions grow. This is the inevitable result when church decisions are made based on human wisdom, human creativity, and human innovation rather than the revealed Word of God.
Other excerpts from the book: