He is mentioned in the Epistles of St Paul (Romans 16:14). He served as a bishop in the first-century Church, and died a martyr. His book, The Shepherd, is one of the earliest Christian writings outside of the New Testament, and was held in such esteem by the early Church that it is sometimes found in ancient collections of the Holy Scriptures.

Hermas had been a wealthy man, but had fallen into poverty through his sins. A man, clad all in white and holding a staff, appeared to St Hermas and, telling him that he was an angel of repentance, gave St Hermas twelve commandments:

To believe in God

To live in simplicity and innocence

To love truth and flee from falsehood

To guard his thoughts in chastity

To learn patience and magnanimity of soul

To know that a good and an evil spirit attend every man

To fear God, but not the devil

To perform every good deed and to restrain himself from every evil one

To pray to God in faith from the depths of his heart, so that his prayer might be heard

To preserve himself from melancholy, the daughter of doubt, and from anger

To try true and false prophecies

To preserve himself from every evil desire.