Pope Leo the Great on Advent Observance

And while all seasons are opportune for this duty, beloved, yet this present season is specially suitable and appropriate, at which our holy fathers, being Divinely inspired, sanctioned the Fast of [December], that when all the ingathering of the crops was complete, we might dedicate to God our reasonable service of abstinence, and each might remember so to use his abundance as to be more abstinent in himself and more open-handed towards the poor. For forgiveness of sins is most efficaciously prayed for with almsgiving and fasting, and supplications that are winged by such aids mount swiftly to God’s ears…

Pope Leo the Great, From Sermon XVI: On the Fast of the Tenth Month