75 Because of human liberty and of events beyond all human control, the efforts of even the holiest of men will sometimes fail. But a priest ought to remember that in the mysterious counsels of Divine Providence, the eternal fate of many men is bound up with his pastoral interest and care and the example of his priestly life. Is not this thought powerful enough both to stir up the lackadaisical in an effective way and to urge on to greater efforts those who are already zealous in the work of Christ?
Source: Sacerdotii Nostri Primordia (Vatican.va)