The first thing he wrote down was the procedure that Jesus used to make apostles, priests, and teachers.
Mormon says that Jesus came to call sinners to repentance, but children are not capable of committing sin.
In Moroni chapter 9, his father Mormon reports that he is still alive, but the Lamanites were victorious in battle, and a number of leading Nephites have been slain.
Still, these atrocities pale in comparison to those of the Nephites in Mariantum, who availed themselves of the daughters of the Lamanites, tortured them to death, and ate their flesh.
Mormon asks his son, rhetorically, how God could be expected to withhold judgment from such a people.
In 421 CE, Moroni wrote a few more things before adding his plates to the ones his father sealed up in the hill Cumorah.
And if they ask with a sincere heart, the truth of them will be made manifest through the power of the Holy Spirit.