The early history of Christianity was marked by blood covenants - rituals involving the blood of believers or animals, which was used to bond worshippers and to symbolize the life of Jesus.
Use of blood in religious rites and ceremonies has a long history, with examples present in the Middle East and Africa, and even in parts of Europe. While many of these practices pertained to ancient pagan beliefs - for instance between believers in the Norse God Odin - some instances of the blood covenant are Jewish in origin. Early Christian groups, in particular the Gnostics who worshipped Christ in a clandestine manner in Rome, are considered to have partaken in blood covenants to a limited extent.
The notion of a blood covenant between two believers was as a bond between them; the strength of this bond was increased further by the symbolic presence of blood in the life of Jesus. However, knowledge of the practice reached the enemies of Jews and early Christians, who exaggerated the ceremonial use of blood as justification for religious persecutions.
Henry Clay Trumbull was a Christian minister and author who had access to a wide range of sources; the fact that the blood covenant had hitherto been overlooked by scholars of Christianity spurred him to publish this book.