We could preach a thousand sermons on this verse and never exhaust the glory of its truth -
I do not frustrate the grace of God: for if righteousness come by the law, then Christ is dead in vain.
In brief -
I shall not frustrate (set aside) grace (the teaching of it, the living in it, or the rejoicing about it)
for, it righteousness (right-standing, forgiveness, salvation)
come by the law (my obedience, my ability, my goodness as measured against another, my attention to detail, my religious affiliation)
then Christ is dead (crucified) in vain (for nothing, for no purpose, for no reason).
Bottom line – God had a perfect law – and a world filled with broken, imperfect people. So, he gave his perfect Son – that He might redeem and reconcile those people to Himself. He does so, not based on the goodness of those people – but based on the Goodness of that One Person, Jesus.
If we could have been made right with God by keeping any law – any form of it, any interpretation of it, any rabbinical application of it, any religious permutation of it – then Jesus would not have died. In fact, His death would have been foolish – because He would have done something for us that we could have done for ourselves.
He entered into our broken circumstances – and took upon Himself our sin, our separation, our guilt, our pride, our foolishness, our ignorance, our brokenness – and He died (for us… as us?)
This is grace. This is love-that-has-no-bounds. This is oceans of mercy and rivers of peace. This is awesome, period. This is God.
But… Why? So that we could then, post-salvation, having believed this truth, saddle ourselves with MORE law-keeping, more religion, more stuff-to-make-God-happy-so-He-won’t-get-me? Heaven forbid!
We are to live FREE – both from religion AND sin. We are to recognize, rightly, the harmful things in this world – but we do so with a “sound mind” – and not a “timid heart”. We walk as sons and daughters of God, brothers and sisters of Christ. We have His heart – and He holds our future. We live by the Spirit – and we walk by the Spirit – heirs of eternity – forgiven, graced with mercy, alive… and well!