In our place, Christ is both “covenant-breaker” and “covenant-keeper”–He endured the punishment we deserved and secured the righteousness we could never obtain.
“God requires two things of us: punishment for our sins and perfection in our lives. Our sins must be punished, and our lives must be righteous. But we cannot bear our own punishment (Ps. 49:7-8), and we cannot provide our own righteousness. ‘None righteous; no, not one (Rom. 3:10).
“Therefore, God, out of his immeasurable love for us, provided his own Son to do both. Christ bears our punishment, and Christ performs our righteousness. And when we receive Christ (John 1:12), all of his punishment and all of his righteousness is counted as ours (Rom. 4:4-6; 5:1, 19; 8:1; 10:4; 2 Cor. 5:21; Phil. 3:8-9).”
Praise God for the sin-bearing death of Christ, who gave His life so that we might obtain ours!
 John Piper, This Momentary Marriage (Wheaton: Crossway, 2009), 46.