The following is from Luther’s “Preface to the Book of Romans,” to which John Wesley was listening at a meeting on Aldersgate Street when he found his heart “strangely warmed.”
Faith is a living, unshakeable confidence in God’s grace; it is so certain, that someone would die a thousand times for it. This kind of trust in and knowledge of God’s grace makes a person joyful, confident, and happy with regard to God and all creatures. This is what the Holy Spirit does by faith. Through faith, a person will do good to everyone without coercion, willingly and happily; he will serve everyone, suffer everything for the love and praise of God, who has shown him such grace. It is as impossible to separate works from faith as burning and shining from fire. Therefore, be on guard against your own false ideas and against the chatterers who think they are clever enough to make judgments about faith and good works but who are in reality the biggest fools. Ask God to work faith in you; otherwise you will remain eternally without faith, not matter what you try to do or fabricate.
1. Martin Luther, Preface to the Book of Romans (Franklin, TN: Seedbed, 2016), 14-15.