The ground or basis of our justification is the righteousness of Jesus Christ—his perfect obedience to the law for us, his sufferings and death in our place. The instrument or God-given means by which we appropriate justification is faith, which is God’s gift to us. The fruit of justification is good works because the justified believer is also sanctified, so that he is no longer ungodly: he is no longer wicked, profane, and devoid of any piety or reverential awe toward God. Instead, being justified by faith alone without works, he is sanctified and brings forth fruit, much good fruit, to the glory of the God who justified him, even to the glory of the God who graciously justifies the ungodly.
In justification, then, we have no plea except the perfect obedience, sufferings, death, and righteousness of Jesus Christ. In justification, when we stand before the holy, righteous God, we say, “I am ungodly, but Christ is just and righteous. I have sinned, but Christ has been perfectly obedient. I am guilty, but Christ is innocent and he has made perfect satisfaction for my sins.” In justification we say, “My conscience [accuses] me that I have grossly transgressed all the commandments of God, and kept none of them, and [I] am still inclined to all evil” (Heidelberg Catechism, A 60).