Why is trying to keep the commandments through good works a mistake?
Trying to keep the commandments through good works is a mistake because it puts people into bondage, legalism, and law-keeping, causing them to give up freedom and joy. It is groveling in good works instead of realizing Christ died and paid it all. It is the opposite of grace.
Les explains that legalism leaves people crawling in the dust, begging that somehow they can make it. The Galatians were going back into that kind of law-keeping, giving up their freedom and joy and getting wrapped up again in legalism. Paul asks how they could desire to again be in bondage. Les says the human race is still groveling in legalism and good works, trying to keep the commandments, and not realizing that when Christ died, He paid it all. The mistake is returning to bondage instead of resting in the finished work of Christ.