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 them 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 act of evangelical obedience. They are justified wholly and solely because God imputes to them Christ’s righteousness. He imputes to them Christ’s active obedience to the whole law and his passive obedience in death. They receive Christ’s righteousness by faith, and rest on him. They do not possess or produce this faith themselves; it is the gift of God.
Faith which receives Christ’s righteousness and depends on him is the sole instrument of justification, yet this faith is not alone in the person justified, but is always accompanied by all the other saving graces. And it is not a dead faith, but works by love.
Christ, by his obedience and death, fully discharged the debt of all those who are justified, and by the sacrifice of himself through the blood of his cross, underwent instead of them the penalty due to them, so making a proper, real, and full satisfaction to God’s justice on their behalf. Yet because he was given by the Father for them, and because his obedience and satisfaction were accepted instead of theirs (and both freely, not because of anything in them), therefore they are justified entirely and solely by free grace, so that both the exact justice and the rich grace of God might be glorified in the justification of sinners.
From all eternity God decreed to justify all the elect, and Christ did, in the fullness of time, die for their sins, and rise again for their justification. Nevertheless, they are not personally justified until the Holy Spirit, in due time, actually applies Christ to them.
God continues to forgive the sins of those who are justified, and although they can never fall from the state of justification, yet they may because of their sins, fall under God’s fatherly displeasure. In that condition they will not usually have the light of God’s countenance restored to them until they humble themselves, confess their sins, ask for pardon, and renew their faith and repentance.
The justification of believers during the Old Testament period was in all these respects exactly the same as the justification of New Testament believers.