Therefore, having been justified by faith, we have[a] peace with God through our Lord Jesus Christ, 2 through whom also we have access by faith into this grace in which we stand, and rejoice in hope of the glory of God.
def to aquit, pardon, to declare righteous
It is a legal term used to depict a favorable verdict from a judge.
In salvation, when a person repents and believes on Jesus for forgiveness of sin God not only pardons the believing sinner but also bestows to the believer His own righteousness.
The act of God in justifying a believing sinner consists of taking away the guilt and penalty of sin, since Jesus took both on Himself on the cross, and imputes His righteousness. Thus declaring the believing sinner both guiltless and positively righteous for time and eternity.