58 This lofty aspect of doctrine is what the Church has in mind when, with maternal care, she invites her sacred ministers to devote themselves to asceticism and urges them to celebrate the Eucharistic Sacrifice with the greatest possible interior and exterior devotion. May not the fact that some priests fail to keep in mind the close connection that ought to exist between the offering of the Sacrifice and their own self-dedication be the reason why they gradually fall off from that first fervor they had at the time of their ordination? St. John Vianney learned this from experience and expressed it this way: "The reason why priests are remiss in their personal lives is that they do not offer the Sacrifice with attention and piety." And he, who in his lofty virtue, was in the habit of "offering himself as an expiation for sinners" (67) used to weep "when he thought of the unhappy priests who did not measure up to the holiness demanded by their office" (63)
Source: Sacerdotii Nostri Primordia (Vatican.va)