Two years afterwards, when certain of the opinions of Luther were violently attacked by the Faculty of Paris, Melancthon interposed to defend their author, to repel some vain charges which were brought against him, and to ridicule the pride and ignorance of the doctors of the Sorbonne. About the same time he engaged in the more delicate question respecting the celibacy of the clergy, and opposed the Popish practice with much zeal and learning. This was a subject which he had always nearest his heart, and, in the discussions to which it led, he surpassed even Luther in the earnestness of his argument; and he at least had no personal interest in the decision, as he never took orders. In 1528 it was determined to impose a uniform rule of doctrine and discipline upon the ministers of the Reformed churches; and the office of composing it was assigned to Melancthon. He published, in eighteen chapters, an ‘Instruction to the Pastors of the Electorate of Saxony,’ in which he made the first formal exposition of the doctrinal system of the Reformers. The work was promulgated with the approbation of Luther; and the article concerning the bodily presence in the Eucharist conveyed the opinion of the master rather than that of the disciple. Yet were there other points so moderately treated and set forth in so mild and compromising a temper, as sufficiently to mark Melancthon as the author of the document; and so strong was the impression produced upon the Roman Catholics themselves by its character and spirit, that many considered it the composition of a disguised friend; and Faber even ventured to make personal overtures to the composer, and to hold forth the advantages that he might hope to attain by a seasonable return to the bosom of the Apostolic Church. The Diet of Augsburg was summoned soon afterwards, and it assembled in 1530, for the reconciliation of all differences. This being at least the professed object of both parties, it was desirable that the conferences should be conducted by men of moderation, disposed to soften the subjects of dissension, and to mitigate by temper and manner the bitterness of controversy. For this delicate office Luther was entirely disqualified, whereas the reputation of Melancthon presented precisely the qualities that seemed to be required; the management of the negotiations was accordingly confided to him. But not without the near superintendence of Luther. The latter was resident close at hand, he was in perpetual communication with his disciple, and influenced most of his proceedings; and, at least during the earlier period of the conferences, he not only suggested the matter, but even authorised the form, of the official documents.