The doctrine of justification, the storm-center of the Reformation, was for Paul the heart of the gospel (Rom. 1:17; 3:21-5:21; Gal. 2:15-5:1), shaping his message (Acts 13:38, 39) and his devotion (2 Cor. 5:13-21; Phil. 3:4-14). Though other New Testament writers affirm the same doctrine in substance, the terms in which Protestants have affirmed and defended it for almost five centuries are drawn primarily from Paul.

Justification is God's act of pardoning sinners and accepting them as righteous for Christ's sake. In it, God puts permanently right their previously estranged relationship with Himself. this justifying sentence is God's bestowal of a status acceptance for Jesus' sake (2 Cor. 5:21).

God's justifying judgement seems strange, for pronouncing sinners righteous may appear to be precisely the kind of unjust action by a judge that God's own law forbids (Deut. 25:1; Prov. 17:15). Yet it is a just judgement, for its basis is the righteousness of Jesus Christ. As "the last Adam" (1 Cor. 15:45), our representative head acting on our behalf, Christ obeyed the law that bound us and endured the punishment for lawlessness that we deserved, and so "merited" our justification. Our justification is on a just basis (Rom. 3:25, 26; 1 John 1:9), with Christ's righteousness reckoned to our account (Rom. 5:18, 19).

God's justifying decision is in effect the judgement of the Last Day regarding where we will spend eternity, brought forward into the present and pronounced here and now. It is a judgement on our eternal destiny; God will never go back on it, however much Satan may appeal against the verdict (Zech. 3:1; Rom. 8:33; Rev. 12:10). To be justified is to be eternally secure (Rom. 5:1-5; 8:30).

The necessary means of justification is personal faith in Jesus Christ as crucified Savior and risen Lord (Rom. 4:23-25; 10:8-13). Faith is necessary because the meritorious ground of our justification is entirely in Christ. As we give ourselves in faith to Jesus, Jesus gives us His gift of righteousness, so that in the very act of "closing with Christ," as older Reformed teachers put it, we receive the divine pardon and acceptance we can find nowhere else (Gal. 2:15, 16; 3:24).

Historic Roman Catholic theology includes sanctification in the definition of justification, considered as a process rather than a single decisive event, and affirms that while faith contributes to our acceptance with God, our works of sanctification and merit must contribute too. Catholics see baptism as conveying the sanctifying grace that first justifies us. Afterward the sacrament of penance allows supplementary merit to be achieved through works, securing justification if the grace of God's initial acceptance is lost through mortal sin. This supplementary merit does not oblige God to be gracious although it is the normal context for receiving it. On the Roman Catholic view, believers effect their own salvation with the help of the grace that flows from Christ through the church's sacramental system. The Reformers pointed out that this view of salvation undercuts the sense of confidence that only free grace can provide to those who have no merits. Paul had already showed that all people, of whatever piety, are without merit, and need a free justification if they are to be saved. A justification that needs to be completed by the recipient is no resting place.

Sproul, R.C. Justification and Merit. The Reformation Study Bible. Orlando: Ligonier Ministries. 2005. 1695