Those whom God effectually calleth, he also freely justifieth: 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; nor 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.
—The Westminster Confession of Faith, Chapter 11, Point 1
Via: Paul Helm