At this point the story has ended. The comparison has been set, and now Nephi turns to explicitly condemning his brothers. He had just accused Laman and Lemuel of being murderers in their hearts. Now he continues to describe their unrighteousness.
The brothers have heard the voice of God as a still small voice, but they were past feeling. In this, Nephi describes the way that God speaks through the Holy Ghost to the majority of his children. It is in an impression rather than a dramatic declaration. Nevertheless, if we can feel that Spirit, we may know its source. The hardened heart is, by definition, past feeling.
Lehi had seen that Laman and Lemuel would not partake of the fruit of the tree of life. Nephi declares that he too, subsumed under the influence of the Spirit, also feels anguish for them.