Only Faith Justifies

God does everything to justify us. Christ has merited our justification, and the Holy Spirit implements the merit of Christ, so that we are justified. The Word, as well as the Sacrament and the preacher, is the instrument through which the Holy Spirit effects the implementing of this merit of Christ. But actual justifying is left to faith alone, since without faith neither God nor Christ nor anything else is profitable for righteousness.

Source: Quoted in Ewald M. Plass, What Luther Says, A Practical In-home Theology for the Active Christian. St. Louis: Concordia Publishing House. 1959 Edition, 10th Printing (1994), p. 707.