Formerly titled "An Epistle to the Inhabitants of New Castle and Berwick, 1558," one subheading reads; "John Knox to the Inhabitants of Newcastle and Berwick, and Unto All Others, Who Sometime in the Realm of England Professed Christ Jesus, and Now Be Returned to the Bondage of Idolatry, Wishes True and Earnest Repentance By the Power and Operation of That Same Spirit Who Called From Death Jesus, the Only Pastor of Our Souls."

Written to stem the tide of backsliding and compromise during the dark days of Mary's reign in England, Knox sends a pastoral exhortation of repentance to those who had reverted to idolatrous worship. Grieving, he says that he was "wounded almost to death" over these developments.

Nevertheless he remained faithful to his readers, directing them to consider the great reward awaiting those who persevere and noting "how horrible are the torments which the slaves of Satan (I mean idolaters, and such as for fear refuse the known truth) shall suffer with the Devil, and with his angels, without end."

Herein we see the serious nature of idolatry and of turning away from truth once attained.