How do we know that legalism is dangerous?

Legalism is dangerous because it subtly alters the gospel message and introduces a reliance on human works for salvation. Paul warns against this in his letters, highlighting that any mixture of law and grace fundamentally denies God's grace. The legalist may proclaim grace but ultimately introduces conditions that revert back to works. This can fracture the peace and assurance that comes from being justified by faith alone. By falsely asserting that righteousness can come from legal adherence, legalists not only undermine their own faith but also pose a grave threat to the soul's well-being of others, as they obscure the redemptive work of Christ and suggest that His sacrifice was insufficient without our own merit.