Most religious movements wait generations for a systematic account of their own beliefs, usually written by an outside scholar long after the movement's founders are gone. Oneness Pentecostalism did not wait. In 1983, David K. Bernard published The Oneness of God, a book length argument that God is one indivisible person who reveals himself as Father, Son and Holy Spirit rather than three eternally distinct persons in one Godhead. Bernard was not an outside observer. He went on to become General Superintendent of the United Pentecostal Church International, the largest Oneness Pentecostal body in the world, and the book was published by Word Aflame Press, UPCI's own denominational press, headquartered in the same Missouri city as the church's own international offices.
The book became the founding volume of a series in Pentecostal Theology and stayed in print for decades, reissued through the 1980s and 1990s with a revised edition in 2000. It is, in the plainest sense, the movement explaining itself to itself, a task it handed not to an academic but to the person who would go on to lead it.
That combination of insider authorship and sustained scholarly engagement is unusual enough that it drew outside academic attention. Amos Yong, a scholar at Fuller Theological Seminary working outside the Oneness Pentecostal tradition, credited Bernard's body of work, of which this book is the first entry, with marking what Yong called the emerging maturation of the Oneness Pentecostal academy. Bernard later went further still, chairing the Oneness side of a formal Trinity-Oneness Dialogue convened by the Society for Pentecostal Studies, putting the doctrine this book first laid out into direct scholarly conversation with the Trinitarian theology it argues against.
A movement's own theology, written by its own future leader, tested later in open dialogue with the tradition it disagrees with: that arc, beginning to end, runs through one book.