Faith is a living, well-founded confidence in the grace of God, so perfectly certain that it would die a thousand times rather than surrender its conviction. Such confidence and personal knowledge of divine grace makes its possessor joyful, bold, and full of warm affection toward God and all created things—all of which the Holy Spirit works in faith. Hence, such a man becomes without constraint willing and eager to do good to everyone, to serve everyone, to suffer all manner of ills, in order to please and to glorify God, who has shown toward him such grace. It is thus impossible to separate works from faith—yea, just as impossible as to separate burning and shining from fire.
A great definition of faith from Luther. I gather this is from his preface on Romans. I have not got a copy of that so I have not cross checked. Luther’a definition of faith is excellent because it captures all the elements. Faith is a gift of divine grace that enables us to believe God based on what we know. It is not static but a living faith that is evidence in good works!