What is justification?
Justification is an act of God's free grace unto sinners,1 in which he pardoneth all their sins, accepteth and accounteth their persons righteous in his sight;2 not for any thing wrought in them, or done by them,3 but only for the perfect obedience and full satisfaction of Christ, by God imputed to them,4 and received by faith alone.5
Scripture proofs
The Westminster Assembly's proof texts (KJV). The bracketed numbers in the answer above mark the clause each set of references supports; expand a row to read the verses.
1 Rom. 3:22, 24–25; Rom. 4:5
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:
Rom. 3:24 Being justified freely by his grace through the redemption that is in Christ Jesus:
Rom. 3:25 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;
But to him that worketh not, but believeth on him that justifieth the ungodly, his faith is counted for righteousness.
2 2 Cor. 5:19, 21; Rom. 3:22–25, 27–28
2 Cor. 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.
2 Cor. 5:21 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:
Rom. 3:23 For all have sinned, and come short of the glory of God;
Rom. 3:24 Being justified freely by his grace through the redemption that is in Christ Jesus:
Rom. 3:25 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;
Rom. 3:27 Where is boasting then? It is excluded. By what law? of works? Nay: but by the law of faith.
Rom. 3:28 Therefore we conclude that a man is justified by faith without the deeds of the law.
3 Titus 3:5, 7; Eph. 1:7
Titus 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;
Titus 3:7 That being justified by his grace, we should be made heirs according to the hope of eternal life.
In whom we have redemption through his blood, the forgiveness of sins, according to the riches of his grace;
4 Rom. 4:6–8; Rom. 5:17–19
Rom. 4:6 Even as David also describeth the blessedness of the man, unto whom God imputeth righteousness without works,
Rom. 4:7 Saying, Blessed are they whose iniquities are forgiven, and whose sins are covered.
Rom. 4:8 Blessed is the man to whom the Lord will not impute sin.
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.)
Rom. 5:18 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.
Rom. 5:19 For as by one man’s disobedience many were made sinners, so by the obedience of one shall many be made righteous.
5 Acts 10:43; Gal. 2:16; Phil. 3:9
To him give all the prophets witness, that through his name whosoever believeth in him shall receive remission of sins.
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.
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:
This doctrine across the Standards
Where the Confession and the Westminster Shorter Catechism treat the same matter, so the question can be studied alongside its parallel statements.
In the Westminster Confession
XI.1 Those whom God effectually calleth he also freely justifieth; not by infusing righteousness into them, but by pardoning …
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.
→ XI.1 · Of JustificationXI.2 Faith, thus receiving and resting on Christ and his righteousness, is the alone instrument of justification; yet is …
Faith, thus receiving and resting on Christ and his righteousness, is the alone instrument of justification; yet is it not alone in the person justified, but is ever accompanied with all other saving graces, and is no dead faith, but worketh by love.
→ XI.2 · Of JustificationXI.3 Christ, by his obedience and death, did fully discharge the debt of all those that are thus justified, …
Christ, by his obedience and death, did fully discharge the debt of all those that are thus justified, and did make a proper, real, and full satisfaction to his Father's justice in their behalf. Yet inasmuch as he was given by the Father for them, and his obedience and satisfaction accepted in their stead, and both freely, not for anything in them, their justification is only of free grace; that both the exact justice and rich grace of God might be glorified in the justification of sinners.
→ XI.3 · Of JustificationXI.4 God did, from all eternity, decree to justify all the elect, and Christ did, in the fulness of …
God did, from all eternity, decree to justify all the elect, and Christ did, in the fulness of time, die for their sins, and rise again for their justification: nevertheless, they are not justified until the Holy Spirit doth, in due time, actually apply Christ unto them.
→ XI.4 · Of JustificationXI.5 God doth continue to forgive the sins of those that are justified; and although they can never fall …
God doth continue to forgive the sins of those that are justified; and although they can never fall from the state of justification, yet they may by their sins fall under God's fatherly displeasure, and not have the light of his countenance restored unto them, until they humble themselves, confess their sins, beg pardon, and renew their faith and repentance.
→ XI.5 · Of JustificationXI.6 The justification of believers under the Old Testament was, in all these respects, one and the same with …
The justification of believers under the Old Testament was, in all these respects, one and the same with the justification of believers under the New Testament.
→ XI.6 · Of JustificationXIV.2 By this faith a Christian believeth to be true whatsoever is revealed in the Word, for the authority …
By this faith a Christian believeth to be true whatsoever is revealed in the Word, for the authority of God himself speaking therein; and acteth differently upon that which each particular passage thereof containeth; yielding obedience to the commands, trembling at the threatenings, and embracing the promises of God for this life and that which is to come. But the principal acts of saving faith are accepting, receiving, and resting upon Christ alone for justification, sanctification, and eternal life, by virtue of the covenant of grace.
→ XIV.2 · Of Saving FaithIn the Westminster Shorter Catechism
Q.33 What is justification?
Justification is an act of God's free grace, wherein he pardoneth all our sins, and accepteth us as righteous in his sight, only for the righteousness of Christ imputed to us, and received by faith alone.
→ Open Q.33