I, Zeniff, having been taught in all the language of the Nephites,

Mosiah 9:1 I, Zeniff, having been taught in all the language of the Nephites, and having had a knowledge of the land of Nephi, or of the land of our fathers’ first inheritance, *and having been sent as a spy among the Lamanites that I might spy out their forces, that our army might come upon them and destroy them—but when I saw that which was good among them I was desirous that they should not be destroyed.

I think this scripture is interesting because he seems to be copying Nephi's method of starting his story.  Perhaps this became the cultural way to start a story, kind of like, Once upon a time....

"their doings shall be as a stumbling block"

Mosiah 7:29 For behold, the Lord hath said: I will not succor my people in the day of their transgression; but I will hedge up their ways that they prosper not; and their doings shall be as a stumbling block before them.

Very interesting.  Our actions can cause us to stumble.  When we do things that are not right, it creates problems for us.  Of course it does.

One way of looking at wickedness is to call it chaos and to call righteousness order or peace.  Chaos never leads to order or peace.  Imagine I have a container full of black marbles on the top and white marbles on the bottom.  It is organized and peaceful.   If I shake it the marbles will blend and be all mixed up, in chaos.  If I keep shaking this container for a thousand years, will the marbles ever go back to their sorted state?  No.  Never. The only way to sort the marbles again is to put some focused intelligence into sorting, take them by hand and sort them again.

So  if we are wicked, or causing chaos in our lives, it will cause our lives to be disorganized and we will stumble.    Our actions affect who we are.  Our actions do not define who we are, but they affect it.  Who we are is our being, our personality, our essence.  This is the part of us that will stumble.  The becoming, the being part of us will stumble because of our actions.  If our actions were who we were then the statement that  our doings shall be a stumbling block would not make sense.  It would make sense to say, that person is stumbling, you can see it by their actions.  But no, the part of us that stumbles is our soul.  Our actions are things that happen in time.  We exist continually, through time.

Why is the word ceremony used in Mosiah 19:24?

Mosiah 19:23-24

 23 And the people told the men of Gideon that they had slain the king, and his priests had fled from them farther into the wilderness.

  24 And it came to pass that after they had ended the ceremony, that they returned to the land of Nephi, rejoicing, because their wives and their children were not slain; and they told Gideon what they had done to the king.

I think the ceremony has to do with the death of the king and they are obligated to do some ceremony as quickly as possible, thus they don't wait until they return to the land of Nephi.

I agree with this site:

The fact that "the ceremony" is mentioned only in passing and is not described suggests that it was such a normal thing that there was no need to explain it. I believe that these Nephites, who had just slain their king and perhaps others in battle, underwent the purification required under the law of Moses for those who had touched dead bodies.

This site had some interesting insights:

the conversation itself is a ceremony or that it involved some kind of cere­monial aspect in recounting the execution of King Noah.

I don't think so.  The article also suggested that,

a word might have been miscopied or misheard as cere­mony

They suggest the word was sermon, misspelled as cermon, and then fixed incorrectly to be ceremony.  I don't think so.  I think there really was a ceremony and Mormon was just in a hurry to finish the text and fit it all in and he figured it was obvious so he didn't go into more details.

Someone Else's Blog Why is the word ceremony used in Mosiah 19:24?