Monergism

Those whom, God effectually calls he also freely justifies, not by infusing righteousness into them, but by pardoning their sins, and by accounting and accepting their persons as righteous; not for anything wrought in them or done by them, but for Christ’s sake alone; not by imputing faith itself, the act of believing, or any other evangelical obedience to them as their righteousness, but by imputing the obedience and satisfaction of Christ unto them, they receiving and resting on him and his righteousness by faith, which faith they have not of themselves, it is the gift of God
Westminster Confession of Faith (11.1)

Justification is a judicial act of God, in which He declares, on the basis of the righteousness of Jesus Christ, that all the claims of the law are satisfied with respect to the sinner
L. Berkhof Systematic Theology (pg. 513)