Why does God sometimes allow priests and bishops to be overcome by their own passions and weaknesses?

St. John Chrysostom often pointed out that God allows priests and bishops to be overcome by their weaknesses and passions so that they may learn from their weaknesses to be compassionate with sinners, and to forgive others. This happened to St. Peter in the New Testament and Elijah the prophet in the Old Testament.¹⁷⁰⁸ This does not mean, however, that God provides excuses for the sins of the priests: “The sin to which the priest consents may be committed by many seculars, but his chastisement shall be far more severe.”¹⁷⁰⁹