Dr. Dan Doriani is an EPC pastor in St. Louis (& professor at Covenant Seminary). We've been talking a lot about legalism in the last few weeks. I came across this excellent explanation that he gives. I hope it is helpful...
“Class-one legalists are auto-soterists; they declare what one must
do in order to obtain God’s favor or salvation. The rich young ruler was
a class-one legalist.
Class-two legalists declare what good deeds or spiritual disciplines
one must perform to retain God’s favor and salvation.
Class-three legalists love the law so much they create new laws, laws
not found in Scripture, and require submission to them. The Pharisees,
who build fences around the law, were class-three legalists.
Class-four legalists avoid these gross errors, but they so accentuate
obedience to the law of God that other ideas shrivel up. They reason,
‘God has redeemed us at the cost of his Son’s life. Now he demands our
service in return. He has given us his Spirit and a new nature and has
stated his will. With these resources, we obey his law in gratitude for
our redemption. This is our duty to God.’ In an important way this is
true, but class-four legalists dwell on the law of God until they forget
the love of God. Worshiping, delighting in, communing with, and
conforming to God are forgotten.
Class-four legalists can preach sermons in which every sentence is
true, while the whole is oppressive. It is oppressive to proclaim Christ
as the Lawgiver to whom we owe a vast debt, as if we must somehow repay
him- – repay God! — for his gifts to us.
I count myself a member of the legion of recovering class-four
legalists. We slide into a ‘Just Do It’ mentality occasionally,
dispensing commands just because they are right.