True faith is not idle. We can therefore, ascertain and recognize those who have true faith from the effect or from what follows. WA 39I, 114; LW 34, 183Works are a certain sign, like a seal on a letter, which makes me certain that my faith is genuine. As a result if I examine my heart and find that my works are done in love, then I am certain that my faith is genuine. WA 10III,225.Love is evidence of faith and gives us firm and certain confidence in the mercy of God; thus we are commended to make our calling certain by good works (II Peter 1:10). WA 39II,248.Works assure us and bear witness before men and the brethren and even before our own selves that we truly believe and that we are sons of God in hope and heirs of eternal life. WA 39I, 293.
I went to Althaus' book after I listened to some pastor being interviewed. Clearly, according to Althaus, Luther considered the certainty of salvation as partially dependent on this new obedience. It is sad when Lutheranism is portrayed by its own adherents as if it was antinomian. Luther, the name from which the denomination got its name, was none of that.