Martin Luther was right in the 16th century in answering the question: what happens at the moment of salvation?Though faith in Jesus Christ alone and by God's matchless grace alone, God forgives the sinner.
And...
God imputes (=credits, reckons) Christ's perfect righteousness to the sinner as if it were the sinner's own.
Thus, when the sinner recognizes his own sin and his own need of divine grace to rescue him from eternal judgment and he places his faith in Jesus Christ alone recognizing that He took the Father's wrath on the cross in the place of the deserving sinner. Thus, God forgives the sinner. At the same time, God doesn't just forgive the sinner and leave him "neutral." He imputes to that sinner all of Christ's perfect righteousness as if it were the sinner's very own perfection. Thus, the sinner receives an "alien righteousness."
This is the gift of God in salvation. "Salvation is of the LORD" (Jonah 2:9).
