For where the great unfathomable love and favor of Christ are known and believed, thence flows forth also love both to God and to our neighbor. For by means of such knowledge and consolation the Holy Spirit moves the heart to love God, and gladly does what it should to his praise and thanks, guards against sin and disobedience and willingly offers itself to serve and help everybody, and where it still feels its weakness it battles against the flesh and Satan by calling upon God, etc. And thus while ever rising in faith it holds to Christ, where it does not do enough in keeping the law, its comfort is that Christ fulfills the law and bestows and imparts his fullness and strength, and thus he remains always our righteousness, salvation, sanctification, etc.
This is the right way to secure the observance of the law, of which our blind critics know nothing; but Christ beautifully shows by this, that one must hear the Gospel and believe in Christ before he can fulfill the law; otherwise there is nothing but hypocrisy and nothing but pure boasting and talking about the law without any heart and life in it all.
Martin Luther, Second House Postil for the Thirteenth Sunday after Trinity (Luke 10:23-37)