Our website has a couple of good articles on Saint Leo the Great. I wrote one here. It includes part of the Tome he wrote for the Council of Chalcedon, to which Dr. Marshall refers. Another article is here from our From the Housetops magazine. One must read the entire Tome to appreciate the importance of this Christological treatise. It was truly inspired. Just google Tome of Saint Leo the Great.
Dr. Taylor Marshall: In order to prepare for Lent, I was looking at the Lenten sermons of Pope Saint Leo the Great (died AD 461).
In his Sermon 46 on Lent, he exhorts the faithful to fast from food and luxury and vain thoughts. And then he goes further and exhorts them to give up heresy for Lent:
For the mind then only keeps holy and spiritual fast when it rejects the food of error and the poison of falsehood, which our crafty and wily foe plies us with more treacherously now, when by the very return of the venerable Festival, the whole church generally is admonished to understand the mysteries of its salvation.
Read article here.