Just a Spark of Faith 

On earth the heart can never attain or feel faith to such a degree as it should; but it always stays in the state of a wishing and a sighing of the spirit, too deep for a man to express. Then the heart says: "Oh, that it were true!" Again: "Ah, if only one could believe it!", etc.

Nevertheless, this sighing and this spark of faith achieve so much that God regards them as a complete faith and says: "According to your faith be it unto you; and because you believe, you are certainly saved."

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. 487.