For God has done what the law, weakened by the flesh, could not do. By sending his own Son in the likeness of sinful flesh and for sin, he condemned sin in the flesh, in order that the righteous requirement of the law might be fulfilled in us, who walk not according to the flesh but according to the Spirit. (Romans 8:3—4; ESV)
Verse 4 is somewhat complicated. God sent his Son so that sin could be dealt with in the body of Jesus “in order that the righteous requirement of the law might be fulfilled in us.” The difficulty is that, “the righteous requirement of the Law” must refer to something good and positive because it is fulfilled in us who walk according to the Spirit. I believe Paul is saying that Jesus fulfilled the Law and paid the price for our sins in the offering of his body so that we would do what is right. Jesus did not die so that we would go into sinful living. Jesus died so that we would be justified and thus live for what is right. I believe Paul’s point here in Romans 8:4 is the same as Galatians 5:13-14.
For you were called to freedom, brothers. Only do not use your freedom as an opportunity for the flesh, but through love serve one another. For the whole law is fulfilled in one word: “You shall love your neighbor as yourself.” (Galatians 5:13—14; ESV)
What is the righteous requirement of the Law of Moses? Love the Lord your God with all your heart and to love your neighbor as yourself. Paul is saying that Jesus offered himself up for our sins so that we would live righteous lives, not sinful lives. Paul is tying back in the message of Romans 6. We cannot sin thinking that in doing so grace is abounding. We cannot sin because we are not under the Law of Moses but under grace. We have been set free to serve God and one another, not to serve sin.