Calvin: To Admit Sinner into Union with God is to Justify Him...

"Hence the Apostle shows that man is at enmity with God until he is restored to favor by Christ, (Romans 5:8- l 0.) When the Lord, therefore, admits him to union, he is said to justify him, because he can neither receive him into favor, nor unite him to himself, without changing his condition from that of a sinner into that of a righteous man. He adds that this is done by remission of sins. For if those whom the Lord has reconciled to himself are estimated by works, they will still prove to be in reality sinners, while they ought to be pure and free from sin. It is evident therefore, that the only way in which those whom God embraces are made righteous, is by having their pollutions wiped away by the remission of sins, so that this justification may be termed in one word the remission of sins." [emphasis added]

Calvin, John. Institutes: Christian Religion Book 3.9.22