Greg Beale defines typology as “the study of analogical correspondences among revealed truths about persons, events, institutions, and other things within the historical framework of God’s special revelation, which, from a retrospective view, are of a prophetic nature and are escalated in their meaning” (Handbook on the New Testament Use of the Old Testament, pg. 14 – an excellent resource, by the way!).
To put it another way, there are times when the Old Testament foreshadows something or someone in the New Testament. Usually, these “types” are not clear until we see their deeper fulfillment in the NT. Beale also convincingly argues that there are usually clues in the wider context of the original passage that indicates the character or event is typological. Thus, the original author wouldn’t have objected to Matthew or John or Paul seeing a “fuller meaning” in Jesus of that type.
(On a side note, Beale also points out that typology worked within the OT as well, not just between OT and NT. He points to the example of Noah as a typological fulfillment of Adam and the “day of the LORD” prophecies in the prophets; pg. 16. This establishes a basis for typology being a normal method of biblical interpretation and biblical prophecy that was developed well before the NT writers made use of it.)
The reason this discussion is relevant is due to Paul’s use of the Hagar/Sarah story in Galatians 4:21-31. Paul calls his method “allegorical” (4:24), but as we saw in the sermon, that word was transliterated, not translated, and we should be careful not to impose modern conceptions of a word’s meaning into its ancient usage. It is not so simple to say that Paul saw the Hagar/Sarah story in Genesis 16 as “allegorical,” for what we mean by “allegory” and what Paul meant by using the word are likely two different things.
It’s also not so simple to say that Paul’s method of interpretation was strictly “typological.” It was not merely analogy or illustration either. I’m not positive we have a great category for what Paul does with Hagar and Sarah in Galatians 4. Perhaps it’s somewhere in between allegory and typology.
What is clear is that 1) Paul sees the Hagar/Sarah story as a historical event, not merely allegory of some deeper spiritual truth, and 2) Paul sees the events between the women and their respective sons as, in some way, picturing a grander truth with the old Mosaic Covenant and the New Covenant.
I love D. A. Carson’s characteristic frankness when he discusses the passage in his article “Galatians 4: The Gospel of Grace: How to Read the Bible” (pgs. 87-107 in Christ Has Set Us Free: Preaching & Teaching Galatians; quote from pg. 100-1): “Some find ‘allegorical’ exegesis a bit spongy and uncontrolled, but sort of smile and say, ‘Well, you know it is Paul the apostle writing this, and he had the gift of the Spirit, so he can pronounce his judgment that this is what the Old Testament narratives really meant. We can’t do the same because we don’t have the same authority.’
“Or they say, ‘Well, transparently, Paul’s exegesis here is allegorical; it’s figurative. But that’s because he is deploying an ad hominem argument that might convince his readers, even if it doesn’t convince us. It’s not the usual way Paul handles Scripture. This time Paul is quietly lowering the bar to their level of intellectual attainment.’
“These are the sorts of excuses we design to help Paul out of the hole he has dug for himself. But such arguments simply won’t account for verses 21 and 30. Paul is convinced he is arguing from Scripture, and he rebukes the Galatians for not seeing what he sees in Scripture, for what he holds to be transparently there.” Well said! Again, any attempt to pigeonhole or characterize Paul’s exegesis in Galatians 4 with simple, modern-day labels will fall short of what Paul actually does with the text. It’s best to go along with the ride and attempt to grasp his point rather than figure out the means of his getting there.