Source: Robert L. Reymond, A New Systematic Theology of the Christian Faith, 2d ed., rev. and updated (Thomas Nelson, 1998), 742-43.

Justification refers to God’s wholly objective, wholly forensic judgment concerning the sinner’s standing before the law, by which forensic judgment God declares that the sinner is righteous in his sight because of the imputation of his sin to Christ, on which ground he is pardoned, and the imputation of Christ’s perfect obedience to him, on which ground he is constituted righteous before God. In other words, “for the one who does not work, but believes in him who justifies the ungodly” (Rom. 4:5), God pardons him of all his sins (Acts 10:43; Rom. 4:6-7) and constitutes him righteous by imputing or reckoning the righteousness of Christ to him (Rom. 5:1, 19; 2 Cor. 5:21). And on the basis of his constituting the ungodly man righteous by his act of imputation, God simultaneously declares the ungodly man to be righteous in his sight. The now-justified ungodly man is then, to employ Luther’s expression, simul iustus et peccator (“simultaneously righteous and sinner”).

The doctrine of justification means then that in God’s sight the ungodly man, now “in Christ,” has perfectly kept the moral law of God, which also means in turn that “in Christ” he has perfectly loved God with all his heart, soul, mind, and strength and his neighbor as himself. 

It means that saving faith is directed to the doing and dying of Christ alone (solus Christus) and not to the good works or inner experience of the believer.  It means that the Christian’s righteousness before God is in heaven at the right hand of God in Jesus Christ and not on earth within the believer. It means that the ground of our justification is the vicarious work of Christ for us, not the gracious work of the Spirit in us. It means that the faith-righteousness of justification is not personal but vicarious, not infused but imputed, not experiential but judicial, not psychological but legal, not our own but a righteousness alien to us and outside of us (iustitia alienum et extra nos), not earned but graciously given (sola gratia) through faith in Christ that is itself a gift of grace. It means also in its declarative character that justification possesses an eschatological dimension, for it amounts to the divine verdict of the Eschaton being brought forward into the present time and rendered here and now concerning the believing sinner. By God’s act of justifying the sinner through faith in Christ, the sinner, as it were, has been brought, “before the time,” to the Final Assize and has already passed successfully through it, having been acquitted of any and all charges brought against him! Justification then, properly conceived, contributes in a decisive way to the Calvinistic doctrine of assurance and the eternal security of the believer.