In the book On the Preacher and Preaching (a letter to Andre Fremyor, archbishop of Bourges), Saint Francis de Sales begins with The Preacher. In addition to living a holy and sacramental life, the preacher must avoid every form of extravagance so as to stand beyond reproach.
Nugae saecularium sunt blasphemiae clericorum. Things that are mere trifles among laymen are blasphemous acts among the clergy. --Saint Bernard
Oportet episcopum esse irreprehensibilem. 1Tim. 3:2 The overseer (bishop) must be beyond reproach.
Pope Francis is exemplary in impressing the need for our preachers and christian teachers to be lovers of poverty! Clerics must lead simple and even austere lives. This is a gospel that the world readily embraces. Men of God should guard themselves against the thirst for wealth by rejecting everything superfluous.
One way to do this, ironically, is by requiring clerics to dress always in clerical garb. Bishops in the United States and throughout Europe should impose fines on clerics and religious who go out in public as if they were lay people! That alone would reverse the God-less tide of our present world and of our clergy, beginning with our bishops!
Thanks be to God that in this Catholic moment it is once again the Supreme Pontiff who is pointing the way!
Priests should manifestly live priestly lives 24/7, the habit helps you acquire the habit.
N.B. In the same book cited above Saint Francis lists authors to be read for sermon content. Some of the authors are more available than others but the list is especially interesting for those who have the leisure to browse through Spanish, French or Italian theological libraries. I'm sure both Popes would have easy access to all of those works in the Vatican Libraries and Archives.
Saint Thomas Aquinas
Saint Antoninus, O.P. (1389-1459) Archbiship of Florence. Summa theologiae moralis, Summa confessorum, Iuris pontificii et caesarei summa.
Bishop William of Lyons (Gulielmus Peraldus, Lugdunensis, etc.), O.P. (1190-1255) Summa de virtutibus et vitiis.
Father Bernardino Rossignolo, S.J. (1563-1613) De actionibus virtutis, ex s. scrituris et patribus libri duo (Venice, 1603).
Philip Diez, (sixteenth century Spanish Franciscan [+1601]), Summa praedicantium, and also his sermons. Canciones quaruplices in Evangelia.
Hieronymus Orosius (1506-1580), O.P. Portuguese, bishop of Sylves. Paraphrases et commentarii in s. scripturam.
Louis de Granada's, O.P. (1555-1588) spiritual works.
Maurice Hylaret's, Franciscan (1539-1591), sermons.
Diego Stella's, Spanish Franciscan (1524-1595) commentary on Luke.
Alfonso Salmeron, S.J. on the Gospels.
Sebastian Barradas, S.J. on the Gospels.
"Saint Gregory excels among the ancients."
Saint Chrysostom
Saint Bernard