It seems to me that the distinction between primary and secondary doctrines is implicit rather than explicit in Scripture. But I think the distinction is still very clear. Here, briefly, are five biblical arguments in favor of making some kind of distinction between primary and secondary doctrines:
- Jesus Himself suggested that some errors are gnats and some are camels (Matt. 23:24-25). And He stated that some matters of the law are "weightier" than others (v. 23). Think about it; such distinctions could not be made if every point of truth were essential.
- Paul likewise speaks of truths that are "of first importance" (1 Cor. 15:3)—clearly indicating that there is a hierarchy of doctrinal significance.
- Certain issues are plainly identified by Scripture as fundamental or essential doctrines. These include:
- doctrines that Scripture makes essential to saving faith (e.g., justification by faith—Rom. 4:4-5; knowledge of the true God—Jn. 17:3; the bodily resurrection—1 Cor. 15:4; and several others).
- doctrines that Scripture forbids us to deny under threat of condemnation (e.g., 1 Jn. 1:6, 8, 10; 1 Cor. 16:22; 1 Jn. 4:2-3).
Since these doctrines are explicitly said to make a difference between heaven and hell while others (the "gnats" Jesus spoke of) are not assigned that level of importance, a distinction between fundamental and secondary truths is clearly implied.
- Paul distinguished between the foundation and that which is built on the foundation (1 Cor. 3:11-13). The foundation is established in Christ, and "no other foundation" may be laid. Paul suggests, however, that the edifice itself will be built with some wood, hay, and stubble. Again, this seems to suggest that while there is no tolerance whatsoever for error in the foundation, some of the individual building-blocks, though important, are not of the same fundamental importance.
principle Paul sets forth in Roman 14 also has serious implications for
this question. There were some differences of opinion in the Roman
church which Paul declined to make into hard-and-fast matters of truth
vs. heresy. In Romans 14:5, he writes, "One man esteemeth one day above
another: another esteemeth every day alike. Let every man be fully
persuaded in his own mind." That clearly allows a measure of tolerance
for two differing opinions on what is undeniably a point of doctrine.
As an apostle, Paul could simply have handed down a ruling that would have settled the controversy. In fact, elsewhere he did give clear instructions that speaks to the very doctrine under debate in Romans 14 (cf. Col. 2:16-17). Yet in writing to the Romans, he was more interested in teaching them the principle of tolerance for differing views on matters of less-than-fundamental importance. Surely this is something we should weigh very heavily before we make any point of truth a matter over which we break fellowship.