Faith is a living, bold trust in God's grace, so certain of God's favor that it would risk death a thousand times trusting in it. Such confidence and knowledge of God's grace makes you happy, joyful and bold in your relationship to God and all creatures. The Holy Spirit makes this happen through faith. Because of it, you freely, willingly and joyfully do good to everyone, serve everyone, suffer all kinds of things, love and praise the God who has shown you such grace.
An Introduction to St. Paul's Letter to the Romans fromDr. Martin Luthers Vermischte Deutsche Schriften. Johann K. Irmischer, ed. Vol. 63(Erlangen: Heyder and Zimmer, 1854), pp.124-125. (EA 63:124-125)