Maynard assembles a chronological and bibliographical history of the Comma Johanneum from early patristic and versional evidence through the medieval Latin tradition, Erasmus and the printed Greek text, Reformation controversy, and modern criticism. He defends the authenticity of the traditional wording of 1 John 5:7–8 and treats related disputes such as 1 Timothy 3:16, using facsimiles, long quotations, manuscript reports, theological controversy, and an extensive bibliography.

The volume is a major archive of older sources and remains valuable even to readers who reject its conclusion. Its research quality is reduced by uneven evaluation of the evidence: possible allusions are sometimes treated as direct testimony, manuscript and versional statistics require updating, and the concluding account supplements textual argument with speculative narratives about Satan, Romanism, liberalism, and the theology or character of opponents.