Daniel Bolliger has a very perceptive article “Bullinger on Church Authority: The Transformation of the Prophetic Role in Christian Ministry” (Architect of Reformation pp159-177). Not only does he give a detailed account of Bullinger’s Karlstag sermon delivered on 28 January 1532 but he also compares this with his analysis of Bullinger’s De prophetae officio (30 June 1525).
Bolliger points out the covenant context to Bullinger’s view of the prophet in the church:
“This dialectic of teaching and defending did not necessarily draw out the more attractive aspects of this new pastoral side to the prophetic office. Bullinger, therefore, connected the pastoral and teaching aspects through another essential development indicated in De prophetae officio: covenant theology. Bullinger clearly applied covenant theology bot in his teaching on scriptural interpretation and in his treatment of the pastoral office of the prophet.
Already in 1523, referring to Romans 10:4, Bullinger cautiously employed the traditional term testamentum (covenant), in his writing. At the beginning of his interpretation of the letter to the Hebrews in 1526 he openly declared that the New Testament is the fulfillment of the covenant with Israel. He then proceeded further in this direction by responding to a question which, although only implicitly posed in the 1532 oration, was present in all the new disciples of the humanist philosophia christiana of the 1520’s: if the New Testament is the important part of the Bible, what is the purpose of the rest of scripture? Bullinger’s answer lay in the covenant of God and humanity, culminating in God’s testament in Christ, which is the overall status of scripture as a whole. Therefore, and correspondingly, the status of every precept, story, periscope or letter, in short, of every passage of the Bible refers, if adequately interpreted, to this great basic status (the covenant). The prophet is responsible for linking the traditional medieval understanding of the divine covenant or testament with the new principle of scriptural sufficiency. This unity, according to Bullinger, is only possible through the adoption of a new methodological approach, which is the true task of the prophet.”