Having shown the law to be something so very opposite to the promise of justification by faith, Paul now answers another commonly asked question in vv.21-22.
Is the law then contrary to the promises of God? Certainly not! For if a law had been given that could give life, then righteousness would indeed be by the law. But the Scripture imprisoned everything under sin, so that the promise by faith in Jesus Christ might be given to those who believe.
Is there conflict, then? Is the law contrary to the promises of God? Paul uses the strongest terms possible to say certainly not! (μὴ γένοιτο, not at all, never, God forbid!)
Both were given by God, but for different purposes (cf. Romans 8.34, Deuteronomy 8.1). If they are not in conflict, then how are they in harmony, how do they work together? How do law and the promise go hand in hand?
The law shows the utterly unattainable, heavenly high, spotless and supreme standards required by an all-together holy God in order to be accepted by Him. This is what Paul means by saying Scripture imprisoned everything under sin. Remember, Scripture to Paul is what we would call the Old Testament: the law, the prophets, and the writings. That part of our modern Bibles really does set the standard and show sin to be sin. It shows us, when we look at it and then ourselves honestly, that all have sinned and fall short of the glory of God (Romans 3.23). Simply, the law and its standards force us to accept that, do you know what, we need help with this. As much as we don’t like to admit to needing help with anything, confronted with the truth that we are imprisoned…under sin, we do need to find a solution, we do need to find salvation from this situation.
In then comes the promise by faith in Jesus Christ. When we finally give up our futile attempts to prove to God how worthy we are and admit that we will never get there, there is promised salvation on offer through faith in Jesus: who He is, what He did, His faithfulness, His ability to meet the standard, His death, and His resurrection.
Today, stop trying to earn and deserve acceptance from God. It’s already there waiting for you, it’s promised to you, it’s available to you by faith in Jesus Christ.