John Calvin said, “…a man will be justified by faith when, excluded from righteousness of works, he by faith lays hold of the righteousness of Christ, and clothed in it, appears in the sight of God not as a sinner, but as righteous…”
No man will see the beauty of necessity of justification by faith until he understands that he is excluded form righteousness of works, that in himself he is able only to merit condemnation. But as Calvin said when once a man knows himself to be excluded from righteousness by works he is able to take hold of the righteousness of Christ offered him in the gospel by faith. He then can with joy and confidence stand before God as righteous.
The Westminster Confession section 11 sets forth the wonderful doctrine of justification.
Section 1 tells us:
-That those God effectually call to Christ he also freely justifies. It is a gift of grace through Christ that he freely, that is willingly bestows on sinners.
-That God does not justify by infusing righteousness into us. The Roman Catholic’s teach that we are justified when God works righteous in us (infuses us with righteousness) by his Spirit by enabling us to obey him such that we may be declared righteous. Thus justification is ultimately on the grounds of our works rather than the work of Christ. We deny that this is the bible’s teaching.
-That in fact God does not justify us for anything at all done in us or by us but only on the basis of what Christ has done as our representative which is received by faith alone. Even the faith God gives us as a gift and works in us that we might believe in Christ is merely the instrument by which we take hold of Christ and does not contribute in any way to our justification. Instead saving faith receives and rests upon Christ and his righteousness alone by faith. We must not turn our faith or any other grace wrought in us into a work that we do that contributes to our justification. Christ and his work is the sole and all sufficient grounds of our acceptance with God.
-That God justifies us by pardoning our sins and counting and receiving us as righteous in his sight on the basis of Christ’s work alone. He credits the perfect obedience of Christ to us as the perfect righteousness (fulfillment of the law) he requires and counts the death or Christ to us as a full satisfaction of that punishment which our sins deserve.
in justification God declares those who are not righteous as righteous by crediting the work of Christ to them. God actually declares the ungodly righteous through Christ! (Romans 4:5) How we must fight to believe and receive this grace through Christ. Listen to the words of Reformed theologian Geerhardus Vos from one of his sermons:
“Among all the realities of the invisible world, mediated to us by the disclosures and promises of God, and to which our faith responds, there is none that more strongly calls into action this faculty for grasping the unseen than the divine pronouncement through the Gospel, that, though sinners, we are righteous in the judgment of God. That is not only the invisible, it seems the impossible; it is the paradox of all paradoxes; it requires a unique energy of believing; it is the supreme victory of faith over the apparent reality of things; it credits God with calling the things that are not as though they were; it penetrates more deeply into the deity of God than any other act of faith.”
Westminster Confession 11.1
I. 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 any thing 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.
 ROM 8:30 Moreover whom he did predestinate, them he also called: and whom he called, them he also justified: and whom he justified, them he also glorified. ROM 3:24 Being justified freely by his grace through the redemption that is in Christ Jesus.
 ROM 4:5 But to him that worketh not, but believeth on him that justifieth the ungodly, his faith is counted for righteousness. 6 Even as David also describeth the blessedness of the man, unto whom God imputeth righteousness without works, 7 Saying, Blessed are they whose iniquities are forgiven, and whose sins are covered. 8 Blessed is the man to whom the Lord will not impute sin. 2CO 5:19 To wit, that God was in Christ, reconciling the world unto himself, not imputing their trespasses unto them; and hath committed unto us the word of reconciliation. 21 For he hath made him to be sin for us, who knew no sin; that we might be made the righteousness of God in him. ROM 3:22 Even the righteousness of God which is by faith of Jesus Christ unto all and upon all them that believe: for there is no difference. 24 Being justified freely by his grace through the redemption that is in Christ Jesus. 25 Whom God hath set forth to be a propitiation through faith in his blood, to declare his righteousness for the remission of sins that are past, through the forbearance of God. 27 Where is boasting then? It is excluded. By what law? of works? Nay: but by the law of faith. 28 Therefore we conclude that a man is justified by faith without the deeds of the law. TIT 3:5 Not by works of righteousness which we have done, but according to his mercy he saved us, by the washing of regeneration, and renewing of the Holy Ghost. 7 That being justified by his grace, we should be made heirs according to the hope of eternal life. EPH 1:7 In whom we have redemption through his blood, the forgiveness of sins, according to the riches of his grace. JER 23:6 In his days Judah shall be saved, and Israel shall dwell safely: and this is his name whereby he shall be called, The Lord Our Righteousness. 1CO 1:30 But of him are ye in Christ Jesus, who of God is made unto us wisdom, and righteousness, and sanctification, and redemption: 31 That, according as it is written, He that glorieth, let him glory in the Lord. ROM 5:17 For if by one man’s offence death reigned by one; much more they which receive abundance of grace and of the gift of righteousness shall reign in life by one, Jesus Christ. 18 Therefore as by the offence of one judgment came upon all men to condemnation; even so by the righteousness of one the free gift came upon all men unto justification of life. 19 For as by one man’s disobedience many were made sinners, so by the obedience of one shall many be made righteous.
 ACT 10:44 While Peter yet spake these words, the Holy Ghost fell on all them which heard the word. GAL 2:16 Knowing that a man is not justified by the works of the law, but by the faith of Jesus Christ, even we have believed in Jesus Christ, that we might be justified by the faith of Christ, and not by the works of the law: for by the works of the law shall no flesh be justified. PHI 3:9 And be found in him, not having mine own righteousness, which is of the law, but that which is through the faith of Christ, the righteousness which is of God by faith: ACT 13:38 Be it known unto you therefore, men and brethren, that through this man is preached unto you the forgiveness of sins: 39 And by him all that believe are justified from all things, from which ye could not be justified by the law of Moses. EPH 2:7 That in the ages to come he might shew the exceeding riches of his grace in his kindness toward us through Christ Jesus. 8 For by grace are ye saved through faith; and that not of yourselves: it is the gift of God.