Follow the Prophets
I think the whole purpose of these two chapters is to convince the reader to follow the prophets.
In chapter 9, several times Mormon says that the people were destroyed because the killed the prophets and saints. It is a graphic chapter about those who completely disregarded the prophets. This is quite a warning to us in this day and time.
Chapter 10 talks about how the prophets were correct in their prophecies. It also talks about how blessed those people are who follow the prophets.
There is a fantastic article in the July 200 Ensign (Following the Prophets: A Book of Mormon Perspective) that talks about following the prophets. The author uses the Book of Mormon as an example of how people were blessed by following the prophets and how people were cursed for not following the prophets.
Who can ignore the pleas of Christ for his people to turn to him by repenting?
V. 13 – “return unto me, and repent of your sins”
V. 14 – “come unto me … mine arm of mercy is extended towards you … blessed are those who come unto me.”
V. 21 – “I have come unto the world to bring redemption unto the world, to save the world from sin.”
V. 22 – “whoso repenteth and cometh unto me as a little child, him will I receive … repent, and come unto me ye ends of the earth, and be saved.”
C. 10 V. 6 – “return unto me with full purpose of heart.”
The invitation is clear to those who survived the destruction. They have a chance to begin a new life, if you will. They are given a second chance to repent and make things right.
These verses testify to the mercy of Christ and God. The Nephites were in an awful state of wickedness and were mostly destroyed. After the destruction, they were granted mercy – a chance to change and truly repent of their sins.
As a small note on chapter 10 – verse 18 states that at the “ending of the thirty and fourth year” Christ appeared to the Nephites and Lamanites who remained alive in the land. Remember that the great destruction took place at the beginning of the 34th year. It seems that most of the 34th year, the people were probably repairing and getting their lives back in order when Christ appeared to them at the temple in Bountiful.