Nephi enjoins all to follow the atoning Messiah, the Son of God, along the narrow path. Nephi promises that, should we do so, without hypocrisy and with real intent, that the Holy Spirit will guide us, and we will become more like the Savior. That is witnessed by speaking with the tongue of angels. Speaking with the tongue of angels places us on a parallel with those heavenly beings. They, and we, will shout praises to the Holy One of Israel because we are becoming more like Him as we follow his path.
There is a caution. Nephi also declares that the more we know, the more we are responsible to our understanding. If we progress to the point where we can speak with the tongue of angels, and then turn against God, “it would have been better for you that ye had not known me.” This is the definition of the sin against the Holy Ghost, and consists of denying what one has learned to be undeniably true.