For what the law could not do, in that it was weak through the flesh, God sending his own Son in the likeness of sinful flesh, and for sin, condemned sin in the flesh: 4 That the righteousness of the law might be fulfilled in us, who walk not after the flesh, but after the Spirit (Romans 8:3).
This is clear and beautiful Gospel. What could not be accomplished for God’s people by any obedience on their part, God sent His Son down here to accomplish for them. Notice that it is not a flaw in God’s law that renders it unable to do for us what we need. It is unable because of the flesh. The weakness or “powerlessness” is through or because of our flesh. The law is good, perfect, right and glorious, but it cannot save us because only those who obey that law perfectly are blessed. We are cursed by it. Enter: God’s Son.
The Son, the Lord Jesus Christ did not save us apart from the law, but rendered to the law what we could not. Perfect, sinless obedience. He condemned sin in the flesh, that is, as a man, by not committing any of it. And further, by honoring the law in every aspect, perfectly. This is what is required, and why it is so absurd for man to think of offering to God, anything that they have done, whether it be a service or a decision. Any thought, word or deed of ours falls infinitely short. When we presume to do anything that in and of itself is imagined to be pleasing unto God, we not only insult His holy law, but we trample under-foot the blood of His dear Son, which was shed expressly because we are powerless to do good.
Christ condemned sin in the flesh also by paying the penalty for our sin, the wages of sin being death. Philippians 2:8 And being found in fashion as a man, he humbled himself, and became obedient unto death, even the death of the cross. That’s right, the Lord Jesus Christ not only did for us, as our Representative what we could not, and did not do, but He paid for what we did do, are doing and shall do. My sin is condemned, but I am justified. My heart is shouting as I write it. My lips yearn to tell it to someone. May God use some voice to declare it broadly and clearly.
The very righteousness of the law is fulfilled in us, that is, we are righteous on the law’s own terms. And it is so, not by what we have done in relation to God’s law, but by Him, in what He did for us. God’s righteousness is not fulfilled in us by our walking after the Spirit and not the flesh. The text declares that we walk not after the flesh, but after the spirit, precisely because He condemned sin, in the flesh, for us. Jonah 2:9 But I will sacrifice unto thee with the voice of thanksgiving; I will pay that that I have vowed. Salvation is of the LORD.