42 A certain connection between this virtue and the sacerdotal ministry can be seen even by the light of reason alone: since "God is a Spirit," it is only fitting that he who dedicates and consecrates himself to God's service should in some way "divest himself of the body." The ancient Romans perceived this fitness; one of their laws which ran Ad divos adeunto caste , "approach the gods chastely," is quoted by one of their greatest orators with the following comment: "The law orders us to present ourselves to the gods in chastity - of spirit, that is, in which are all things, or does this exclude chastity of the body, which is to be understood, since the spirit is so far superior to the body; for it should be remembered that bodily chastity cannot be preserved, unless spiritual chastity be maintained." In the Old Law, Moses in the name of God commanded Aaron and his sons to remain within the Tabernacle, and so to keep continent, during the seven days in which they were exercising their sacred functions.
Source: Ad Catholici Sacerdotii (Vatican.va)