This is perhaps the most important subject because no doctrine is more crucial - nor more misunderstood and neglected, even by Protestants- than the biblical doctrine of justification by faith alone. The Bible teaches that any person who truly believes in Jesus Christ as his or her personal Savior from sin at that point is irrevocably and eternally justified. What is justification? Justification is the act of God whereby He not only forgives the sins of believers, but He also declares them perfectly righteous by reckoning or imputing the obedience and righteousness of Christ Himself to them through faith. It might help to look at it this way: If a wealthy uncle deposits a million dollars to the checking account of his young nephew, that money is now the property of his nephew even though the lad never earned it, worked for it, or deserved it. In justification, God "deposits" the righteousness of Christ to the believer's account - He credits the Christian with the moral perfection of His own Son. Justification is a completed act of God, and because it is entirely accomplished by God, once for all, it is not a lifelong process as is personal sanctification (individual growth in holy living). The following Scriptures clearly show that justification is (1) a crediting of righteousness on the basis of a person's faith alone; (2) a completed act of God; and (3) something that occurs wholly from personal merit or good works.

...to the man who...trusts God who justifies the wicked, his faith is credited as righteousness...[How blessed is] the man to whom God credits righteousness apart from works (Romans 4:56, emphasis added).
 

For we maintain that a man is justified by faith apart from works of the Law (Romans 3:28, NASB, emphasis added). (See also Philippians 3:9.)

Therefore having been justified by faith, we have peace with God through our Lord Jesus Christ (Romans 5:1, NASB, emphasis added).

Much more then, having now been justified by His blood,, we Shall be saved from the wrath of God through Him (Romans 5:9 NASB; cf. Romans 9:30-10:4; 1 Corinthians 6:11; Galatians 2:16; Galatians 3:8-9, 21, 24).
 

    Unfortunately, some Catholics have misunderstood the Protestant position here, thinking it means that mere assent to doctrine saves entirely and that Protestants have little concern for good works or sanctification. To the contrary, Scripture is clear that good works and sanctification are crucial - indeed it is the very knowledge of grace itself (in a Protestant sense) that produces good works and growth in holy living (see Ephesians 2:8-10; 1 Peter 5:12; 2 Peter 3:18; Colossians 1:6; cf. Colossian 2:23). But good works and sanctification have nothing to do with our justification. What justification means to Protestants is that believers are to plead the merits of Christ before the throne of God, instead of their own merits. This is why biblical Christians accept the "gift of righteousness" (Romans 5:17) and "glory in Christ Jesus and put no confidence in the flesh" (Philippians 3:3 NASB).
    Justification means that a Christian may be assured that, in God's eyes, he now possesses the perfect holiness necessary to gain entrance to heaven. Why? If the death of Christ forgave all sins and fully satisfied the divine penalty due them, and if God declares believers absolutely righteous on the basis of their faith in Christ, then nothing else is needed to permit their entrance into heaven. Because of justification - i.e., because Christ's righteousness and merit are reckoned to the believer (as far as God is concerned) - the Christian now possesses perfect holiness in this life, and he possesses it from the moment of saving faith. He cannot attain it by himself, nor does he need sacraments, indulgences, the Rosary, or purgatory in order to enter heaven. This is what the biblical doctrine of justification means."