What I mean is this: The law, introduced 430 years later, does not set aside the covenant previously established by God and thus do away with the promise. For if the inheritance depends on the law, then it no longer depends on the promise; but God in his grace gave it to Abraham through a promise.
Thoughts for Today:Paul reminds me of a very skilled attorney who is now winding his way through mountains of evidence to draw a conclusion. He's saying, "If a man's covenant cannot be added to nor taken away from, then the promise of God to save humanity through faith in Christ Jesus would not have been affected by the introduction of the Law which was a subsequent event." (The Law was introduced 430 years after God's promise to Abraham.) The Living Bible paraphrases verse 18 as follows: "If obeying those laws could save us, then it is obvious that this would be a different way of gaining God’s favor than Abraham’s way, for he simply accepted God’s promise."
The Law and the promise are polar opposites. The Law requires effort by us. It is a work and therefore its benefit is payment or compensation for what's been done. On the other hand, the promise is a gift/inheritance. It is received by grace and therefore, by definition is not something earned or deserved. So we are saved either by works (which must be perfect in order to meet God's holiness standard), or by grace, but not a combination of the two.
Questions to Ponder:The mistake many Christians make is to add works to grace. It can be confusing to understand the difference between what we do in response to Christ's sacrifice, and what is done to earn our position in the Kingdom. One is love the other obligation. Which drives your service?