Of all the functions which, according to the Mosaic ritual, the priest had to discharge, none demanded more patient attention or more strict adherence to the divine guide-book than the discernment and proper treatment of leprosy. This fact must be obvious to every one who studies, with any measure of care, the very extensive and important section of our book at which we have now arrived. There were two things which claimed the priest's vigilant care, namely, the purity of the assembly, and the grace which could not admit of the exclusion of any member save on the most clearly established grounds. Holiness could not permit any one to remain in who ought to be out; and on the other hand, grace would not have any one out who ought to be in. Hence, therefore, there was the most urgent need, on the part of the priest, of watchfulness, calmness, wisdom, patience, tenderness, and enlarged experience. Things might seem trifling which in reality were serious, and things might look like leprosy which were not it at all. The greatest care and coolness were needed. A judgment rashly formed, a conclusion hastily arrived at, might involve the most serious consequences, either as regards the assembly or some individual member thereof. This will account for the frequent occurrence of such expressions as the following; namely, "The priest shall look"--"The priest shall shut up him that hath the plague _seven days_"--"And the priest shall look on him the seventh day"--"Then the priest shall shut him up _seven days more_"--"And the priest shall _look on him again_ the seventh day"--"And the priest shall _see him_"--"Then the priest shall _consider_." No case was to be hastily judged or rashly decided. No opinion was to be formed from mere hearsay. Personal observation, priestly discernment, calm reflection, strict adherence to the written Word--the holy, infallible guide-book--all these things were imperatively demanded of the priest if he would form a sound judgment of each case. He was not to be guided by his own thoughts, his own feelings, his own wisdom, in any thing. He had ample guidance in the Word, if only he was subject thereto. Every point, every feature, every movement, every variation, every shade and character, every peculiar symptom and affection--all was provided for, with divine fullness and forethought, so that the priest only needed to be acquainted with and subject to the Word in all things, in order to be preserved from ten thousand mistakes. Thus much as to the priest and his holy responsibilities. We shall now consider the disease of leprosy, as developed in a person, in a garment, or in a house.