St. Augustine of Hippo 
On True Religion [EPUB ebook] 

The text elaborates on the importance of fasting as a spiritual discipline that distinguishes humans from angels and serves as a means to subdue the flesh and cultivate the spirit. It argues that fasting is essential for achieving righteousness and emphasizes the necessity of temperance even in lawful pleasures. The author critiques the disunity among Christians compared to the concord found among pagans worshiping false gods, urging a return to unity in the body of Christ. The text concludes by highlighting the importance of love, charity, and the need to guide heretics back to the truth.