Answer: Justification is an act of God’s free grace unto sinners₁, in which he pardons all their sins, accepts and accounts their persons righteous in his sight₂; not for any thing wrought in them, or done by them₃, but only for the perfect obedience and full satisfaction of Christ, by God imputed to them₄, and received by faith alone.₅

1. Romans 3:22; Romans 3:24-25
2. 2 Corinthians 5:19; 2 Corinthians 5:21; Romans 3:22; Romans 3:24-25; Romans 3:27-28;
3. Titus 3:5; Titus 3:7; Ephesians 1:7
4. Romans 5:17-19; Romans 4:6-8;
5. Acts 10:43; Galatians 2:16; Philippians 3:9

For further study see:

1. WSC 32: What benefits do they that are effectually called partake of in this life?
2. WSC 33: What is justification?
3. WSC 36: What are the benefits which in this life do accompany or flow from justification, adoption, and sanctification?
4. WLC 70: What is justification?
5. WLC 71: How is justification an act of God’s free grace?
6. WLC 77: Wherein do justification and sanctification differ?
7. WCF CHAPTER 11:  Of Justification