How do we know heresy is a sin?

Scripture indicates that heresy is not merely a mistaken belief; it is a sinful disposition towards God's Word. Those who embrace heretical doctrines do so at their own peril, condemning themselves through their choices. In Titus 3:10, the heretic is described as subverted, indicating a perversion of truth that stems from rejecting God's Word. This self-condemnation reinforces the seriousness of heresy as it directly collides with the truth of salvation found in Christ alone. Thus, choosing to deviate from the faith is not just an intellectual error but is fundamentally sinful, as it undermines the gospel message that brings salvation.