Today's Responsorial Psalm is: "Justice shall flourish in his time and fullness of peace forever" (Psalm 72). But now we go deeper. We ask how Jesus will bring this about.
Jeremiah 23:5-8 tells us God will "raise up a righteous shoot (branch) to David. to reign and govern wisely.. In his days Judah shall be saved and Israel dwell in security."
The O Antiphon tells us this will come about through the wisdom of his laws: "O Leader of the House of Israel, giver of the law to Moses on Sinai.." But Jesus does not save us by laws alone. The antiphon continues, "come to rescue us with your mighty power." Good laws can bring about justice, but Jesus does much more than that. The "fullness of peace" he gives is the peace of knowing that our sins have not just been "forgiven" and our lives re-directed, but that our sins have been taken away. They are no longer part of us or of our history. They have been annihilated. No human action can do that.
But in Matthew 1: 18-25 the angel makes it clear that the son of Mary will not be just human: Mary's virginity was proof that Jesus was conceived "through the Holy Spirit." The absence of a human father is proof of the divine Father. Therefore the added name "Emmanuel" means "God with us" literally. The one who came to be with us in Jesus is God Himself.
Joseph is to name the child "Jesus, because he will save his people from their sins." Jesus can do this because he is divine. Our sins are "taken away" - annihilated - because Jesus took us, with our sins, into his body on the cross. When he died we died "in him." When he rose, we rose in him, to live as his continuing, extended risen body on earth, free from sin. Our redemption is a mystery beyond forgiveness: our sins are "taken away" (Galatians 6:15).
All who have risen in Christ are a "new creation" (2 Cor. 9:17). The "old self," the self with sins, "was crucified with him so that the body of sin might be destroyed." We rise with no record of sin to live a new life as Christ (Galatians 2:20).
This is why John calls Jesus the "Lamb of God, who takes away the sin of the world" (John 1:29). Jesus does this through the divine mystery of his death and rising. He is a Savior who gives, not just justice, but "fullness of peace forever."
If you want Jesus to save your life on this earth, use him! Live in him. What saves our lives from veering off to destructiveness is being guided and empowered by the person of Jesus-Emmanuel, "God with us." Interact consciously with him to live and act as his own body.