71 However, to judge with more certainty the young man's fitness for the priesthood and to have successive proofs of his attained maturity on both the human and supernatural levels—for "it is more difficult to conduct oneself correctly in the service of souls because of dangers coming from outside" (119)—it will be advisable to have a preliminary trial period before the observance of holy celibacy becomes something definitive and permanent through ordination to the priesthood. (120)
Source: Sacerdotalis Caelibatus (Vatican.va)