Justification is a legal term. In court, one accused of a crime is either condemned or justified. Based upon the merit of Christ, sinners are justified before God. His sinless life and substitutionary death on the cross for sinners is the basis for our justification. God justifies us "through the redemption that is in Christ Jesus" (Romans 3:24).
God justifies us by faith in Christ. "Therefore, having been justified by faith, we have peace with God through our Lord Jesus Christ" (Romans 5:1). Faith is trust and confidence, relying upon Christ alone. By faith in Christ, sinners are justified with God.
God justifies us by grace through faith in Christ. Faith receives the grace of God in Christ. Faith is the evidence that the believer is justified before God. It is the assurance of faith. "Therefore it is of faith that it might be according to grace, so that the promise might be sure to all the seed" (Romans 4:16).
God justifies us by faith in Christ unto righteousness. The only way a sinner can become righteous before God is by faith alone. Righteousness is the gift of God to us. "But to him who does not work but believes on Him who justifies the ungodly, his faith is accounted for righteousness" (Romans 4:5).