His return to the active duties of the ministry naturally induced him to resume the studies in Speculative Theology which had occupied him at Needham but which had been in large measure interrupted by the business of teaching at Nantwich and Warrington. He now published his _Institutes of Natural and Revealed Religion_, and began the publication of _The Theological Repository_, a collection of papers on theological questions, contributed by himself and a number of neighbouring ministers and others. The work eventually extended to six volumes, three of which were printed whilst he was at Leeds. “_The Theological Repository_,” says the Rev. Charles Wicksteed,[13] “was one of those publications which will always appear from time to time in every body in which there is much activity and much freedom of thought. It had, however, a very slender circulation, and was very little read by any but theologians of the Liberal school. Indeed, it discussed questions which were viewed with terror by many even of the Liberal school itself, because it, in fact, purposely deserted the beaten track of opinion and opened out those questions on which difficulties began to be felt, or on which fresh light was wanted. It aimed at collecting the contributions of free, independent and thoughtful minds—_towards_ correct ultimate decisions, without pretending itself to furnish those decisions. This is ever a position which the bigoted violently resent, which the unlearned cannot understand, on which even the candid and liberal often look with a dissatisfaction not unmingled with fear, but which is, notwithstanding, the essential preliminary of correct settled opinion in every age of thought. It is a position often assumed by the most contemplative and the most thoroughly honest men of the generation, but one which is never understood until the generation which produced and neglected it is passed. If there were not this neutral ground on which inquiring spirits can meet, beyond the hackneyed and settled points in which alone the many are interested, there would be an end to thought, which in a short time would prove an end to active, healthy, influential and tested truth.” Shortly after his removal to Leeds, Priestley avowed himself an adherent to that school of theological opinion which its enemies associate with the name of Fausto Sozzini; that is, he became what has been called a _humanitarian_, or a believer in the doctrine that Jesus Christ was in nature solely and truly a man, however highly exalted by God.