4 that the righteous requirement of the law might be fulfilled in us who do not walk according to the flesh but according to the Spirit.
Verse four is the final verse that expresses our freedom before God. The goal of the death of Christ is to fulfill the just requirement of the law. The Holy Spirit produces the righteousness of the law in the believer’s life.
The word “that” conveys God’s purpose for Jesus’s work on the cross, which was to fulfill the law.
the righteous [just] requirement [singular] of the law
The definite article “the” before “law” indicates that this is the Mosaic Law. The Holy Spirit fulfilled in us what the law could not do. The law cannot justify a sinner or sanctify a saint. Here the emphasis is that the law cannot sanctify a saint. God sanctifies us apart from the law through the Holy Spirit.
The “righteous requirement” refers to the unity of the law, the collective precepts of the law. The word “requirement” is singular, indicating that God’s will is one unit. The idea is that all the law demands is right. The issue is the degree to which sin must be condemned—it must be condemned in its entirety, for the whole of the law bears down on any single action or thought.
The “righteous requirement of the law” is that which satisfies the demands of the law. God condemned sin by Christ so that He might fulfill the sentence of condemnation on us. Jesus brought into effect our justification; the Christian is not the one who brings about this justification by sanctification. The righteous requirement of the law is absolute perfection. It is a perfect righteousness because God is perfectly righteous.
might be fulfilled in us [realized vicariously]
Christ fulfilled all of the requirements of the law “in” us, not by us. He is the only person capable of fulfilling the entire standard of who God is. It is the accomplishment of Christ, not us.
The word “fulfilled” in the Greek indicates that it is God who does the fulfillment (passive voice). It is someone else who does this through us. God did this by putting the curse upon Christ on the cross. Christians now stand before God fully right in His presence. They cannot keep the law in themselves. The issue here is justification, not sanctification.
The gospel establishes the just demands of the law.
The gospel does not take away the right of the law to hold to its standard, for God is the author of the law. The law is an expression of the character of God. God could never change His standards, because He is immutable. The gospel establishes the law because it meets the demands of the law. Jesus met every requirement of the law with His life and death. He fully satisfied the righteousness of the law. Since He fulfilled the law in every respect, the Christian has fulfilled the law in every respect because we are “in Him.” Since we are united with Him, God sees us the same way as He sees Jesus—perfect. God paid the penalty for our sin in Christ.