“If an addition had been forbidden, the prophets and
apostles would have sinned, for they added many things later.” We respond. One must
distinguish between an addition made by human choice and one made by divine
inspiration. The former must be judged as prohibited but certainly not the
latter, for this command was given not to God but to men. Furthermore, the
prophets did not add anything of a different character to the Law but explained
it more fully and brought greater light to the prophecies about the coming
Messiah. (Johann Gerhard, On the Nature of Theology and on Scripture [trans.
Richard J. Dinda; Saint Louis, Miss.: Concordia Publishing House, 2009], 327)