Calvin: Assurance Reposes in Grace Through Faith in Christ...

First I ask, whether there be any sin, however light, that is not inconsistent with the observance of the law? For what vicious thought will creep into the mind of man if it be wholly occupied with the love of God? The law is not satisfied unless God is loved with the whole heart. That men do not therefore cease to be righteous I admit. But why so, but just because they are blessed to whom sin is not imputed? If they insist on being righteous by works, on which their consciences can repose in the sight of God, they, in the first place, subvert faith, and do an insufferable wrong to the grace of God; and, in the second place, they bring no support to their impious doctrine as to possible observance of the law...

John Calvin. Acts of the Council of Trent with the Antidote