So, what is legalism?

Legalism is an attempt to gain favor with God or to impress our fellow man by doing certain things (or avoiding other things), without regard to the condition of our hearts before God. At the root of legalism is the sin of pride, because the legalist thinks that he is able to commend himself to God by his own good deeds.

Invariably, he is only looking at externals, not at his heart. Also, the legalist’s pride motivates him to exalt himself in the sight of others by his outward behavior, again neglecting to see the corruption of his own heart. 

Thus legalism denies human depravity and exalts human ability. As such, it is opposed to the gospel of God’s grace. That’s why both Jesus and Paul clashed with the legalists.

Jesus hates legalism because it does not deal with the condition of our hearts before God.

Steven J. Cole, 1999

https://bible.org/seriespage/lesson-57-why-jesus-hates-legalism-luke-1137-54

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