The parish church was the center of village life and the priest was the natural guardian of the community. It was his business, for example, to see that no undesirable persons lurked in the village,--heretics, sorcerers, or lepers. It will be observed that the priest, besides attending to the morals of his flock, was expected to see to their bodily welfare by preventing the presence of those afflicted with the only infectious disease against which precautions were taken in the Middle Ages.[140] [Sidenote: Other sources of the Church's power.] 81. The unexampled authority of the mediæval Church is, however, only partially explained by its wonderful organization. To understand the hold which it had upon mankind, we must consider the exalted position of the clergy and the teachings of the Church in regard to salvation, of which it claimed to be the exclusive agent. [Sidenote: The exalted position of the clergy.] The clergy were set apart from the laity in several ways. The higher orders--bishop, priest, deacon, and sub-deacon--were required to remain unmarried, and in this way were freed from the cares and interests of family life. The Church held, moreover, that the higher clergy, when they had been properly ordained, received through their ordination a mysterious imprint, the "indelible character," so that they could never become simple laymen again, even if they ceased to perform their duties altogether or were cast out of the Church for crime. Above all, the clergy alone could administer the _sacraments_ upon which the salvation of every individual soul depended. [Sidenote: Peter Lombard's _Sentences_.] Although the Church believed that all the sacraments were established by Christ, it was not until the middle of the twelfth century that they were clearly described. Peter Lombard (d. 1164), a teacher of theology at Paris, prepared a manual of the doctrines of the Church as he found them in the Scriptures and in the writings of the church fathers, especially Augustine. These _Sentences_ (Latin, _sententiæ_, opinions) of Peter Lombard were very influential, for they appeared at a time when there was a new interest in theology, particularly at Paris, where a great university was growing up.[141] [Sidenote: The seven sacraments.]