Why has the Father sent his Son to do what the weakened law could not do? Paul tells us in verse 4.
“in order that the righteous requirement of the law might be fully met in us, who do not live according to the flesh but according to the Spirit.” (Rom. 8:4, NIV)
The law (or probably better, instruction or regulation) of God was not bad; it was corrupted and weakened by sin. Specifically, the sin was that those who agreed to it decided they were better off ignoring the instruction given by Yahweh, and decided they could be god for themselves. It was idolatry through and through.
And, as it always has and always will, idolatry did not lead the Israelites into life, but death.
As we’ve seen, though, through the first three verses of Romans 8, God did not leave his people to their own folly. As difficult as it is to believe, he actually condemned the sin they so horrifically loved, instead of condemning them in it. And, in verse 4, Paul tells us that God id this so that the δικαίωμα (righteous or just) requirements of God’s law would be fulfilled.
Not just filled, however, in the plain, general sense. Fulfilled in those who do not περιπατοῦσιν (walk or live) according to the flesh, but who walk or live according to the Spirit.
You can see the picture Paul is painting with this section of his letter to the Romans. In just four verses, Paul is showing them (and us) that real and true freedom is found in Jesus through the work of the Spirit of God in our lives. We can trust that this is true because: “The Spirit gives life; the flesh counts for nothing” (Jn. 6:63a, NIV).
With all that, why in the world would you and I try to live any other way? Because you and I are not so different from those ancient Israelites who lived thousands of years ago. Sure, we don’t eat like them, talk like them, or even dress like them. But, if there’s one thing we have in common with our fellow humans of old it’s that we love to make gods out of anything or anyone other than the triune God of the Scriptures.
The good news, though…this triune God of the Scriptures has done something about our unwillingness—more than that, our inability—to trust him. He has given us of himself, through the Spirit.