"Now that no one is justified by the Law before God is evident; for, “The righteous man shall live by faith.” (Galatians 3:11)
The doctrine of justification by faith describes the true method by which fallen, sinful men can be officially declared free from the charges of sin, and seen as righteous in the eyes of a faultless, Holy God. To be justified refers to a new standing before God because of the righteousness of Christ.
Justification is a primarily forensic word, meaning that its implications are of a legal nature. It is the act of a judge or judicial authority (in this case, God) actively declaring someone to be found not guilty. As sinners, mankind as a whole is in affront to God. By our sin, we have made ourselves His enemies; fully deserving of His wrath—guilty of breaking His Law in every sense of the word. Because God is just, the penalty must match the crime. His perfect holiness demands a perfect punishment which is eternal torment in hell.
As sinners, we are powerless to change our state. Even our good deeds are seen as filth to God. No amounts of personal accomplishments, good works, or ritualistic religious practices do a thing to change the record of guilt that is to be justly applied to all of our accounts. Christ’s death on the cross, however, formed the perfect sacrifice for our sin. There, He took the wrath of God upon Himself for all who would repent of their sins and believe in Him. Because Christ lived a sinless life, His sacrifice was deemed acceptable to God for our sins. It allowed God to maintain His justness by punishing Christ instead of the believer and also to see the sinner as perfect and unblemished. This is accomplished because the believer is in Christ. When God sees the man, He sees the imputed righteousness of Jesus Christ (I Corinthians 1:2, 30; 6:11; II Corinthians 5:21).
Justification is apart from any virtuous act of man himself (Romans 3:20; 4:6). God is therefore the “justifier of the one who has faith in Jesus” (Romans 3:26).
See also: Romans 4:5; 5:17; 8:33; Psalm 143:2; Isaiah 53:11; Luke 18:9-14.
There are plenty of additional very valuable resources on the Internet and in the stores (and in many Bible-centered pulpits!) to aid you in your understanding and growth.
For we are enriched in Christ, inasmuch as we are members of his body, and are engrafted into him: nay more, being made one with him, he makes us share with him in everything that he has received from the Father. ~ John Calvin