This is a fascinating interchange. The Spirit asks Nephi if he believes that his father saw the tree, and Nephi responds, “Yea, thou knowest that I believe all the words of my father.” Nephi is right in assuming that the Spirit knows his heart. Why then is he being asked this question? The Spirit is giving him an opportunity to testify to his belief.
The Spirit reacts not only with pleasure but also with the declaration that Nephi is blessed “because thou believest in the Son of the most high God.” Why does the Spirit equate Nephi’s declaration of belief in his father’s words as belief in the Son of God? It is because Lehi was testifying that the Atoning Messiah would come. Thus, Nephi’s belief in his father’s words is also belief in his testimony of the Messiah. From this point on, Nephi’s narrative continues to clarify that Lehi’s entire vision was to teach about the mission of the Son of God.
As the “Excursus: The Nephite Understanding of God” (following 1 Nephi 11) discusses, Nephi is following Lehi’s understanding of the Messiah as Yahweh. This verse in the 1830 edition calls the Messiah the “Son of the most high God.” This phrase is shortened to “Son of God” in the next verse (1 Ne. 11:7, 1830 and 1981). Nevertheless, 1 Nephi 11:18 (1830) states that the “virgin whom thou seest is the mother of God, after the manner of the flesh.” No doubt the presence of the “Son of God” in the same chapter that refers to Mary as the “mother of God” was one reason that the verse 18 was changed to “mother of the Son of God.” However, in Nephi’s understanding of the heavens, it is significant that the particular phrase is “Son of the most high God.” The contexts of the two descriptions are different. Yahweh is the son of ’El, or the “most high God.” However, Yahweh is God in his own right and is rightfully recognized as God. While modern Latter-day Saint theology is very precise about the Father-Son relationship in the Godhead, Israel during Nephi’s lifetime was more fluid in its use of those relationships, allowing them to have slightly different meanings when they referred to Yahweh in heaven or to Yahweh as the Messiah on earth.