Pope Paul VI
Sacerdotalis Caelibatus §54
Sacerdotalis Caelibatus: On the Celibacy of the Priest
54 The true, profound reason for dedicated celibacy is, as We have said, the choice of a closer and more complete relationship with the mystery of Christ and the Church for the good of all mankind: in this choice there is no doubt that those highest human values are able to find their fullest expression.
Source: Sacerdotalis Caelibatus (Vatican.va)