"And by Him all that believe are justified from all things, from which ye could not be justified by the law of Moses" (Acts 13:39).
Many Christians today tend to the doctrine of justification as something too "theological" to deal with. But it simply means "declaring to be righteous" a person who had actually been guilty of some offense. It is the prerogative of the judge trying his case to pronounce innocence or guilt as based on the evidence. In the case of sin against a divine law "It is God that justifieth" (Romans 8:33), for He is the Judge.
But how can God both "be just, and the justifier" of one who is obviously guilty—as, indeed, we all are, since "all have sinned" (Romans 3:26,23)? The answer is that we are "justified freely by His grace through the redemption that is in Christ Jesus: Whom God hath set forth to be a propitiation through faith in His blood, to declare His righteousness for the remission of sins . . ." (Romans 3:24-25).
Christ has credited His perfect righteousness to our account and paid the death penalty for all our sins. We are told in the Scripture above cited (Romans 3:24) that we are justified by His grace. Then Romans 5:1 says we are "justified by faith" and Romans 5:9 says we are "justified by His blood." Finally, we are justified by the Holy Spirit. "Ye are washed, . . . sanctified, . . . justified in the name of the Lord Jesus, and by the Spirit of our God" (I Corinthians 6:11).
And all of this is absolutely guaranteed by Christ's victory over death. "Who was delivered for our offences, and was raised again for our justification" (Romans 4:25). As our text assures us, "all that believe are justified from all things" in the eyes of God. In the eyes of men, however, "By works a man is justified, and not by faith only" (James 2:24). HMM