12 And yet it would undoubtedly be both a distortion of the real mind of this same Supreme Pontiff (who was so interested in the sanctity of the clergy) and a contradiction of the perpetual teaching of the Church in this matter, if anyone should dare to infer from this that clerics were any less bound by their office than religious to strive for evangelical perfection of life. The truth is just the opposite; for the proper exercise of the priestly functions "requires a greater interior holiness than is demanded by the religious state." (14) And even if churchmen are not commanded to embrace these evangelical counsels by virtue of their clerical state, it still remains true that in their efforts to achieve holiness, these counsels offer them and all of the faithful the surest road to the desired goal of Christian perfection. What a great consolation it is to Us to realize that at the present time many generous hearted priests are showing that they realize this; even though they belong to the diocesan clergy, they have sought the help and aid of certain pious societies approved by Church authorities in order to find a quicker and easier way to move along the road to perfection.
Source: Sacerdotii Nostri Primordia (Vatican.va)