In Malachi 3:18 the righteous are described as those who serve the Lord. This verse seems to indicate that God’s children are made righteous by serving the Lord (obeying his covenant law). From this verse, then, it would appear that on the day of judgment, those will be declared righteous who serve God, faithfully obeying his law.
But in the New Testament, we read repeatedly that righteousness is not attained by one’s own service to God or by one’s own obedience to his law. Rather, righteousness is through faith in Christ. But there is no contradiction. We must understand that the righteousness we receive from Christ has two aspects to it, the legal and the ethical.
The first aspect to the righteousness we receive from Christ is the legal righteousness that he obtained for us. While he lived on earth, Christ served the Lord God faithfully throughout his life, even unto death. He is the righteous one (1 John 2:1). And his righteousness is legal, imputed to all who through faith seek their salvation in him alone. As a result, all those who by faith are in Christ
are legally regarded by God as righteous, that is, as those who have served the Lord perfectly throughout their lives. It is on the basis of this imputed righteousness of Christ that they escape God’s wrath and are received into God’s favour on the day of judgment.
The second aspect to the righteousness we receive from Christ is the ethical righteousness that he works in us. Through the working of the Holy Spirit, we are transformed into the image of Christ (Romans 8:29, 1 Corinthians 15:49), and Christ is formed in us (Galatians 4:19). As a result of the Spirit’s work, we become a new creation (2 Corinthians 5:17). We begin to live according all the commandments of God, albeit with great weakness and shortcoming. This ethical righteousness is the necessary fruit of salvation, and without it no one will be saved on the day of judgment (Hebrews 12:14, Ephesians 5:5, 1 Corinthians 6:9–10, Revelation 22:15).
Both the legal righteousness obtained for us and the ethical righteousness worked in us are gifts of Christ. The focus of Malachi 3:18 is upon the ethical righteousness that Christ works in us, but it in no way denies, but rather, is the fruit of the legal righteousness that Christ obtained for us.
18 Then once more you shall see the distinction between the righteous and the wicked, between one who serves God and one who does not serve him.