Nephi concludes this sermon by indicating that this is the only way to reach the desired “end.” He seals this discourse with his testimony, and does so by invoking the name of God. This is Nephi’s equivalent of swearing by the name of God, but includes his understanding of the godhead to be three individuals.
Polemical: Nephi pronounces the name of the three, and specifically states that they are one God. At times, this passage has been used to suggest a development in Joseph’s theology from the triune God to a godhead.
I propose that it is rather a legitimate statement of Old Testament style monotheism (with alterations appropriate to the different nature of Book of Mormon revelation). Let me give a little background on the concept of monotheism, a concept central to Old Testament theology, but one frequently misunderstood as we look backward.
In the theological development evidenced in the Old Testament, monotheism stands out as the great innovation of Israelite religion. There is no other early monotheistic society.
Even so, Israel’s monotheism was firmly in the context of a polytheistic world. The God of Israel was a corporate god, unique in his singular and direct relation to that corporate entity. However, the Old Testament is clear that Israel understood that other cultures had gods. They did not dismiss their existence, merely declared the superiority of their god above all others. Monotheism, at least in its roots, was not a belief in a single god to the exclusion of competing gods, but to an exclusive relationship between the corporate god and his people (and the proclamation of the superiority of that god).
Monotheism, and the insistence upon the uniqueness of god in Israelite religion is a direct result of their physical and cultural location in the midst of polytheistic societies. The adamant preaching of the oneness of god forcibly stands in contrast to the multiplicity of competing gods in competing religions (which at times were evident within Israelite culture).
The Book of Mormon provides exactly the same context. Having the Nephites live in Mesoamerica (as a current hypothesis) places them firmly in the same situation as Israel. They were required to stress the oneness of god to separate the concept from the completing pantheons around them. As with the Old Testament, the Book of Mormon theology of monotheism is perfectly appropriate as a response to polytheism.
In contrast, modern Christian society is so firmly comfortable with their one god, that the clarification of the nature of the godhead is not confusing, and is certainly no temptation to the worship of a pantheon. In the context of the culture which surrounded the Nephites, it makes much more sense to see this passage as a monotheistic affirmation amidst polytheism than as an example of Joseph’s changing theology.