“The Reformation understood theology as critical reflection interior to the church’s mission of proclamation. Thus the Reformation’s claim can be summarized by a parody of the catholic formula: lex proclamandi lex credendi, “the law of proclaiming is the law of believing.” Theology is to take for its rule the specific character by which the gospel is the gospel and not some other sort of discourse; theology must be thinking that guards the proclamation in this authenticity.
“…Surely both formulas are needed (lex orandi lex credendi and lex proclamandi lex credendi). When the Reformation’s rule from proclamation is not followed, theology slips from its assignment. When the catholic rule from prayer is not followed, theology slips from its object, for it is in the church’s prayer and praise, in their verbal form and in the obtrusively embodied forms called sacrifice, that the church’s discourse turns and fastens itself to God as its object.”
–Robert Jenson, Systematic Theology Volume 1: The Triune God, 13-14
Lutheran Theology: An Online Journal 