From Trustful Surrender to Divine Providence: The Secret of Peace and Happiness by Fr. Jean Baptiste Saint-Jure and St. Claude de la Colombière (cf. pp. 15-17).
St. Gregory the Great said that God makes use of men as the doctor does the leeches.
How so?
Doctors, in order to have impure blood drawn from the patient and cure him, order leeches to be applied. Although the leeches’ only aim is to gorge themselves and suck up as much blood as they can, the doctor’s only aim is to cure the patient. There is, therefore, no relation between the insatiable greed of the leeches and the intelligent purpose of the doctor in using them. The patient understands the doctor’s aim. He does not regard the leeches as evildoers. Rather, he tries to overcome the sight of their ugliness and help them in their action, in the knowledge that the doctor has judged it useful for his health.
God, therefore, is like the best of doctors.
He makes use of men as the doctor does of leeches. As God’s patients, we should not focus on the evilness of those to whom God gives power to act on us or be grieved at their wicked intentions. Instead, we should focus on God as our Doctor. He is using them as instruments for our healing. He is the all-good, all-wise, all-powerful God who can use any “leech” of this world to bring about a greater good. God is totally in control. He can “remove” the leech at any moment. Therefore, we should welcome the “leeches” as gifts from God.
Prodigal Catholic 