Often times nowadays we are so keen to get hold of the latest and greatest. The new iPhone is released and people are willing to camp outside the shop in order to be the first to get one. The desire for the upgrade doesn’t stop at phones though. I’ve even heard someone from a fairly major world religion say “Ah yes, yours may have come first, but mine is the upgrade, the newer way, so it’s better…”. It seems as if the Judaizers had a touch of this going on and Paul had to explicitly say that, no, newer is not always better (perhaps you can get your old Nokia 3210 out of the drawer).
Paul is very clear in his goal of showing that justification by faith alone has always been the plan (3.1-14). He says look, when a contract has been signed, that’s that (v.15). He then says that God’s promise to Abraham was always going to find it’s fulfilment in a singular way and in a single person (note the difference between seed/seeds, descendant/descendants, offspring/offsprings) in v.16. Then he shows that in this case the original is still the best, so to speak.
What I am saying is this: The law that came 430 years later does not cancel a covenant previously ratified by God, so as to invalidate the promise. For if the inheritance is based on the law, it is no longer based on the promise, but God graciously gave it to Abraham through the promise.
Paul is saying that look, God’s promise to Abraham was made such so that the inheritance (justification) was given through the promise and received by faith in that promise (v.18).
The point then is that yes, the law did come and it served an important purpose but it did not cancel the previously made agreement, the previously cut covenant, between God and man (v.17). To the churches in Galatia this was another reason to dismiss what the Judaizers were saying about the need to become an outward Jew in order to be really saved and accepted by God. For you and for me, knowing just a little bit of the history of God’s covenants and interactions with His creation can bring a disproportionately high increase in our confidence in His promises, in their veracity, and the One in whom they all find their fulfilment.