The structure of Beckwith’s logical argument is as follows
Premise 1: The Bible teaches that there is only one God.
Premise 2: The Bible teaches that there are three distinct persons called God, known as the Father, Son, and Holy Spirit.
Conclusion: Therefore, the three persons - Father, Son, and Holy Spirit - are the one God.
Beckwith then argues for the truth of Premise 1 and Premise 2, and the Conclusion.
Beckwith adds a section responding to “Oneness” theologians. “Oneness Pentecostalism” argues that the Father, the Son, and the Holy Spirit are not distinct persons who share the same nature and being, but rather, they are the same person. Each title--"Father," "Son," and "Holy Spirit"--represents a different mode by which God, a single person, manifests Himself, just as "uncle," "husband," and "brother" each represents a different mode by which, for example, John Piippo, a single human person, manifests himself. Beckwith states that “this is why the ancient heresy which Oneness embraces is called "modalism."”