They Won't Understand Without the Poetry
Alma wants to explain to the poor Zoramites that they can still worship God even though the snobby Zoramites have banned them from their synagogues. To illustrate his point, he quotes a "prophet of old" named Zenos. The quote is basically to the effect of, "God always heard my prayers and has been merciful to me because of the Atonement." Except that it takes eight verses.
You see, the nuance of Zenos's sermons were important for Alma to relate. Not only did God hear Zenos's prayer when he was in the wilderness, but he also heard Zenos's prayer when he was in his field, in his house, in his closet, in the midst of congregations, and when he had been cast out and despised by his enemies. Sure, you could argue that the passage is poetic, but I think the point is made quite effectively in the first example. Any modern reader would have understood perfectly without some poor Nephite schmuck slaving over a slab of metal to scratch in all the poetic repetitions.
Two Witnesses: Infinitely More Credible Than One
Alma has already quoted one prophet that nobody (except for maybe his original audience) has ever heard of. But he's about to outdo himself by doing the same thing a second time:
For it is not written that Zenos alone spake of these things, but Zenock also spake of these things—Holy crap! You mean Zenos wasn't the only prophet who ever taught about the Son of God?! Hold onto your seats, ladies and gentlemen, because it's going to blow you away when I reveal the other guy you've never heard of—same name, I just changed the soft S at the end to a hard C. Everybody still with me? Okay, it's safe to breathe now.
Finally, in verse 19, Alma provides an example useful for the period in history for which this record was inspired (meaning the present day): Moses. We all know that guy, so we can actually go look up what he taught when Alma references him. But the rest of this stuff was pretty useless.
The Healing Serpent as a Sloppy Type of Christ
Alma also discusses the story from the Book of Numbers of the bronze serpent erected by Moses. A simple glance upward at it would heal any victim of a fatal snake bite. Alma says that there were many who refused to believe the statue could heal them and died because they wouldn't look at it. He then compares this to Christ, claiming that the solution is so simple—look to Christ and live.
This is a terrible comparison.
Take your average Israelite who's been bitten by a snake. He knows he's been bitten and understands that there is a problem and is familiar with the concept of physical death. In his throes of dying agony, he'll probably think, "Hey, I should probably look at that snake. I don't want to die so I'll try anything."
Take your average non-Christian. Assuming Alma's religion is the correct one, this guy has no idea that he's in any danger because he hasn't seen the prospect of Hell slither up to him and sink its fangs into his ankle. He's not familiar with the concept of spiritual death and he has no idea that there's a problem. If he lives to a ripe old age and begins to worry on his death bed, he might think, "Hey, I should probably give this religion thing a chance. I don't know what will happen to me when I die so I'll try anything."
Is that really the attitude Alma expects people to have? I thought he wanted strong, passionate, constantly nurtured faith. His argument seems to consist of "accepting Christ is so easy, you'd be an idiot not to do it." Except that it's really not that easy. Looking at the serpent provides an instantaneous and permanent relief from a lethal ailment. Looking to Christ (at least in Mormonism) requires a constant belief, dedicated church service, plenty of "good works," numerous ordinances, and enduring to the end. It's not as simple as a quick glance at the prophet's sculpture.
Buuuuut I guess if you're trying to convince people to join your silly religion, you'll probably want to make things sound as simple as possible.