Boundaries

Foundations of Faith quotes St Augustine: “In the essentials, unity, in the non-essentials liberty, and in all things charity.” He then lists the categories his professor used to classify doctrine:

• Essential Doctrine 
• Cardinal Doctrines 
• Non-Essentials
• Tertiary and Peripheral

What is essential, and what is not?

Essential Doctrines are doctrines that put you outside of the faith if you deny them. To reject these teachings means you are not a Christian, and the word “Heresy” is usually invoked for this category of error. Examples of essential doctrines are the deity of Jesus Christ, the Trinity, and believing in the bodily resurrection of Jesus. ....

Non-essential doctrines are the ones that usually distinguish denominations. The Baptists, the Presbyterians, and the Pentecostals are all brothers and sisters in Christ. Still, they hold doctrines that are significant enough to impact how they worship and, therefore, opt to attend different churches. Examples of non-essential doctrines include questions such as, “Does the gifts of tongues continue or cease after the Apostles? Predestination or libertarian free will? Baptism—infant or believers? Covenant theology or dispensational? And questions surrounding the rapture. These can significantly impact our worship, but the wrong answers to these questions rarely put us outside of the faith. .... (more)

My denomination—Seventh Day Baptist—holds that the Sabbath should be observed from sunset on Friday to sunset on Saturday, the Biblical Sabbath, but would categorize that belief as important and correct but "non-essential," in the sense that those who disagree with us are not heretics and thus the doctrine belongs in category three of this taxonomy.

Doug Eaton, "4 Categories of Doctrinal Weight in Christian Theology," Fight of Faith, August 20, 2024.