Is it strictly a matter of the issue on the table? Baptism? Lord's Supper? Deity of Christ? The Millennium? Justification? Bodily resurrection? Six literal days of creation? Literal, eternal hell?
Is there any litmus test to these issues that will show which ones are ok to disagree on? I've got two thoughts on this that have proved helpful to me. Here goes nothing.
FIRST, I'm blessed to teach Redemptive History and Systematic Theology. I love explaining the difference to my students. I tell them that RH is the story of God creating and calling a people to be with Him, like Him, and for Him. This is experiential, relational, and more subjective. It is based more on chronology and progressive revelation. A simple way to put it is that RH is about reading the Bible like this:
ST, on the other hand, is asking the question, "What does the Bible say about __________?" Anything can go in the blank: free will, faith, predestination, baptism, etc. ST seeks to grasp what God has revealed about a certain issue throughout the whole of Scripture. ST cannot be done without RH and it is often done flippantly and without regard for the context of how the Spirit breathed out the Scriptures. So, the cute and helpful diagram for how ST reads the Bible is:
Here's the point. If we read the Bible as though we are only and simply in the story of God [RH], we turn into doctrinally spineless loose-nuts who water down the Scriptures and believe that theology damns people and turns them away. Or, if we only read the Bible as a book of doctrines or truths [ST], then everybody else will be wrong except you and your three friends who take Ezekiel out of context and think the Bible's subtitle is "Doctrines You Better Believe."
Some think the tension here is problematic. I think it's perfect. This is a slim part of the reason why Jesus was described as being full of GRACE and TRUTH. So, all I'm saying is that if believers pursue reading the Scriptures correctly, many of the issues that oft divide will find their quirky niche.
This still may not be satisfactory. So,
SECOND, I do believe that there should be a rigid and tenacious contending [Jude 3] for those truths that directly relate to and involve the person and work of Jesus. This doesn't solve everything, but I believe gives us the most wise and safe starting point for juggling these issues. For example,
- the virgin birth
- the historical/bodily resurrection
- the deity of Jesus
- the bodily second coming of Jesus
- the sufficiency of the atonement
These are things to be staunchly defended. There is a centrality to the person and the work of Jesus that cannot be over-articulated and over-delighted in if we are His New Covenant people being His ambassadors in this present, passing age.
There is still plenty of grey room for which we need wisdom. But these two thoughts have helped me see those grey areas as opportunities for humility and not avenues for having to be right.
Hope it helps.