St. Caesarius of Arles (+AD 468-542) , born in Chalon-sur-Saône Eastern France, a very able and well-known Bishop in Merovingian Gaul,a strong proponent of asceticism in the West, having been greatly influenced by St. John Cassian, St. Julius Pomerius, and St. Augustine, and, according to Church historian William Jurgens, was the most influential Bishop in Gaul of his time. As monk of the monastery of Lerins he was a deep contemplative, as well as committed to poverty and distribution to the poor. However, he was also a vigorous opponent of semi-Pelagianism, and even presided over the 2nd Council of Orange in AD 529, which received Papal approval thereafter. His life impacted so many that a 2-volume biography was made of him by 5 close friends. His feast is August 27th, and he is venerated equally by the Catholic and Eastern Orthodox churches.
So much could be adduced from his writings to demonstrate the Patristicity of Catholic doctrine, but I wanted to pull from one of his sermons (Sermo 179) which speaks beautifully to the doctrine of post-mortem purgatorial fire, the need to perform penance, and the danger of hoping for purgatory . He writes:
“Although the Apostle has mentioned many grevious sins, we nevertheless, lest we seem to promote despair, will state briefly what they are. Sacrilege, murder, adultery, false witness, theft, robbery, pride, envy, avarice, and, if it is of long standing, anger, drunkenness, if it persistent, and slander are reckoned in their number. For if anyone knows that any of these sins dominates him, if he does not do penance worthily and for a long time, if such time is given him, and if he does not give abundant alms and abstain from those same sins, he cannot be purged in that transitory fire of which the Apostle spoke [1 Cor 3], but the eternal flames will torture him without any remedy. But since the lesser sins are, of course, known to all, and it would take too long to mention them all, it will be necessary for us only to name some of them. As often as someone takes more than is necessary in food or drink, he knows that this belongs to the lesser sins. As often as he says more than he should or is silent more than is proper; as often as he rudely exasperates a poor beggar; as often as he wills to eat when others are fasting, although he is in good physical health, and rises too late for church because he surrendered himself to sleep; as often as he knows his wife without a desire to have children….without a doubt he commits sin. There is no doubt that these and similar deeds belong to the lesser sins which, as I said before, can scarcely be counted and from which not only all Christian people, but even all the Saints, could not and cannot always be free. We do not, of course, believe that the soul is killed by these sins; but still, they make it ugly by covering it as if with some kind of pustules and, as it were, with horrible scabs, which allow the soul o come only with difficulty to the embrace of the heavenly Spouse, of whom it is written: ‘He prepared for Himself a Church having neither spot nor blemish’…If we neither give thanks to God in tribulations nor redeem our own sins by good works, we shall have to remain in that purgaotrial fire as long as it takes for those above-mentioned lesser sins to be consumed like wood and straw and hay. But someone is saying: ‘It is nothing to me how long I stay there, so long as I go finally to eternal life’. Let no one say that, beloved brethren, because that purgatorial fire itself will be more difficult than any punishments that can be seen or imagined or felt in this life”