Pope Paul VI
Sacerdotalis Caelibatus §18
Sacerdotalis Caelibatus: On the Celibacy of the Priest
18 Consideration of how celibacy is "particularly suited" (12) to God's ministers is not something recent. Even if the explicit reasons have differed with different mentalities and different situations, they were always inspired by specifically Christian considerations; and from these considerations we can get an intuition of the more fundamental motives underlying them. (13) These can be brought into clearer light only under the influence of the Holy Spirit, promised by Christ to His followers for the knowledge of things to come (14) and to enable the People of God to increase in the understanding of the mystery of Christ and of the Church. In this process the experience gained through the ages from a deeper penetration of spiritual things also has its part.
Source: Sacerdotalis Caelibatus (Vatican.va)