What does the Bible mean by 'strange doctrines'?

In Hebrews 13:9, the term 'strange doctrines' refers to teachings that distract believers from the essential truth of the gospel, which centers on Christ. Such doctrines often involve rules or practices that conflict with the grace of God and divert one's focus away from the redemptive work of Christ. Historically, strange doctrines can include legalistic approaches to faith or teachings that promote human effort as a means of gaining salvation, which is contrary to the core message of grace through faith in Jesus Christ. Believers are encouraged to remain steadfast in the truth of the gospel and to be wary of teachings that deviate from the word of God.