It is difficult or impossible to use the Lutheran idea of 'Law and Gospel' as a guide to the theological content of the Bible. The idea has poor biblical support and accounts for a number of ambiguities in Lutheran theology relating to sanctification (including simul justus, 'law always accuses', inabilities to understand the Sermon on the Mount as a message of discipleship). Furthermore, the idea has received quite different interpretations from various Lutheran theologians. However, one fruitful approach is to use 'Law and Gospel' as a guide to measure the impact of a text or message on a specific audience, as is demonstrated with Luther's interpretation of the Sermon on the Mount. But even so, 'Law and Gospel' must be supplemented by the important category of 'discipleship' and other categories in order to encompass the possibilities of the Bible's message.
Hordern, Richard P.
"Law and gospel as hermeneutic: Martin Luther and the Lutheran tradition,"
Consensus: Vol. 9
, Article 1.
Available at: http://scholars.wlu.ca/consensus/vol9/iss1/1