These two verses represent the healing that follows the destruction. These three days balance the three hours. As discussed above (see commentary accompanying 3 Nephi 8:19), although the literal events had different durations—one measurable in hours, the second in days—”three” suggests that this is a constructed time, literarily reinforcing the parallelism of the events.
“In the morning” documents the return of literal daylight; but obviously the symbolism was not lost on Nephi. After the symbolic three days of destruction, a new day dawns. The dissipation of the darkness signals that the destructions are over, as represented by a catalogue of “healing”: “the earth did cease to tremble, and the rocks did cease to rend, and the dreadful groanings did cease, and all the tumultuous noises did pass away, and the earth did cleave together again, that it stood.”
The natural grinding from the earthquake died away, and the human lamentations calmed. Grief for the dead changes to praise of the Messiah.
Redaction: This passage concludes a carefully crafted unit in Nephi’s text. Nephi was not simply reporting what he witnessed but presenting the information in such a way that it communicates the supernal importance of the Messiah’s visit, overriding the destruction.