In verse 16, “...know that a person is not justified by the works of the law (“by observing the law” - NIV 1984), but by faith in Jesus Christ. So we, too, have put our faith in Christ Jesus that we may be justified by faith in Christ and not by the works of the law, because by the works of the law no one will be justified.” You can see how important Paul’s argument was then and even now. What does justified mean? Paul is saying a person is not justified by works but by faith in Christ Jesus. Justify means from the secular dictionary the following: to prove or show to be just or right, to vindicate (of circumstances), to furnish adequate grounds for; to corroborate, to absolve.
From the Word of God we see in Job 9:2 a question, “How should a man be just with God?” Another translation has it this way, “But how can a mortal be righteous before God?” (NIV) So, the Word of God answers that question, however you put it in Habakkuk 2:4, “...but the righteous will live by his faith.” We are justified with God through our faith in Him. Later in the writings of Paul to Galatians in 3:11 we read, “Clearly no one is justified before God by the law, because, “the righteous will live by faith.” Here Paul quotes from Habakkuk 2:4. Warren Wiersbe gives us his definition of justification: “It is the act of God whereby he declares the believing sinner righteous in Jesus Christ.” He continues to say, that justification is an act not a process and that no Christian is “more justified” than another Christian. He goes on and says, quoting Romans 5:1, “Having therefore been once-and-for-all justified by faith, we have peace with God.” (literal translation) Since we are justified by faith, it is an instant and immediate transaction between the believing sinner and God. If we were justified by works, then it would have to be a gradual process.”