God does not owe anything to man. Salvation is a free gift. Grace is not to be confused with law. Men are not saved by keeping the law. They are saved by grace.
Grace saves the worst.
Grace reveals salvation. Therefore, he deserves nothing but God's judgment. Man stands guilty before the bar of God, having broken God's holy law. As such, he is subject to the curse of God. Because he rejected and murdered God's Son, man has no claim on God at all.