Rex theologus : The preachers guard and guide in the didactical part of his duty. Or, A vindication, shewing that the King's Majesty's letter to the late L. Archbishop of Canterbury is most conformable to the judgment and practice of antiquity. Wherein is discuss'd, 1. The duty of preaching in general. 2. To whom it primarily belongs. 3. How managed in the ancient church. 4. What innovations these later times have made.