 Knudsen was a noted hymn poet, and wrote hymn poetry in the traditions of Petter Dass, Thomas Kingo and Grundtvig.Some of his hymns were included in the official hymn books of other churches, and he initially refused to have them admitted in the Norwegian hymn book, although two have later been included.Knudsen wrote a large amount of hymn poetry, and collections of some of his sermons have been printed in books and booklets.