"...Much has been said and much is known of how this holy priest spent untold hours (even to sixteen and more hours a day) in the confessional. That he could “read souls” is well attested by testimony even from before his death. It has even been related that the evil one once cried out, 'If there were two priests like John Vianney, my kingdom on earth would crumble!'..."
On this Feast of St. John Vianney, Fr. Ryan has a really good post for priests: