What are strange doctrines according to the Bible?

Strange doctrines are those teachings that contradict the core tenet of salvation by grace through faith in Christ. In Hebrews 13:9, believers are cautioned not to be carried away by these doctrines. Examples include the belief that one can earn salvation through good works or adherence to the law. These teachings are considered strange because they overlook the sufficiency of Christ's sacrifice and the grace that He offers freely to all who believe. The Apostle Paul consistently emphasized that it is through grace alone—apart from works—that we are saved (Ephesians 2:8-9). Hence, followers of Christ are called to remain steadfast in the true gospel and reject any doctrine that introduces human merit into the equation of salvation.