Attributed to Augustine, the old adage says, “In essentials, unity; in non-essentials, liberty; in all things, charity.” I suspect the wise Christian will heed this advice. Though one wishes to believe that all Christians will agree on every point, our finite and limited perspective will never allow us to have complete understanding of the depth of God’s revealed Word. As such, Christians will disagree at various points along the theological spectrum. The question that then arises is how do we distinguish those areas about which all orthodox Christians must agree (unity) from those about which we may, in a spirit of charity, differ (liberty). I suspect the gospel serves as the dividing line between those issues that are essentials and those that are not.
In his epistle to the Galatians, Paul uses strong language to denounce the unorthodoxy he sees creeping into that church’s thinking (cf. 1:6-9; 3:1). In this example we see the proper means for separating the essential from anything less. One would, I assume, place circumcision on the list of non-essentials. Yet in this letter, Paul argues vehemently for the unimportance of circumcision, consigning to hell (pronouncing anathema) those who force it on Gentile believers. Now, I believe neither circumcision nor uncircumcision matters at all (Galatians 6:15). Still, it mattered at that moment and in that church because it compromised the gospel. If Gentile believers had to become Jews first in order to become Gentiles, then we are saved not by grace but by our works, by upholding the law (an impossible task). Thus, in this setting, circumcision proved essential because the gospel itself was at stake, and so Paul gives no liberty to the Judaizers plaguing the Galatian church (and also publicly rebukes Peter for similar reasons). I think this framework allows us to distinguish the two classes of theological topics.
One might worry at this point that too many doctrines be relegated to the non-essential; after all, what bearing does the doctrine of the Trinity or of Christology (both doctrines many Christians hold to be essential) have on the gospel? But upon closer inspection, we see that each doctrine does cause the gospel to stand or fall. Take Christology as an example: as Gregory of Nazianus argued during the fifth century, “what is not assumed is not healed.” That is, if Christ has not become fully man (including body and mind), he has not fully healed humanity. Indeed, it was precisely Christology’s relationship to atonement (the gospel doctrine) that led Anselm of Canterbury to ask and answer the question “Why did God become man?” Only man can pay the penalty for his sins; only God can offer the infinite penalty needed. Thus, only the God-man (Christ) could effectively satisfy the wrath of God. In my estimation, then, those doctrines necessary to maintain the orthodox gospel are essential, and those that are not, are not.