Monergism

“The gospel is saying that, what man cannot do in order to be accepted with God, this God himself has done for us in the person of Jesus Christ. To be acceptable to God we must present to God a life of perfect and unceasing obedience to his will. The gospel declares that Jesus has done this for us. For God to be righteous he must deal with our sin. This also he has done for us in Jesus. The holy law of God was lived out perfectly for us by Christ, and its penalty was paid perfectly for us by Christ. The living and dying of Christ for us, and this alone is the basis of our acceptance with God.”
- Graeme Goldsworthy, Gospel and Kingdom, p. 86

"In the imputation of Adam’s sin to us, of our sins to Christ, and of Christ’s righteousness to believers, the nature of imputation is the same, so that one case illustrates the other" (Hodge: Systematic Theology, 2:194).

"Therefore, as one trespass led to condemnation for all men, so one act of righteousness leads to justification and life for all men. For as by the one man’s disobedience the many were made sinners, so by the one man’s obedience the many will be made righteous.". (Rom 5:15-18)

Paul is making the point that if Adam's disobedience to the law of God was the reason for death, then Jesus full obedience to all the prescriptions of the divine law unto death is what brings us righteouness.