Alma punches home his point. He has been discussing the Atonement in the abstract, and he now makes it personal. He specifically tells the people of Ammonihah that their hearts are hard, and that they will not enter into the rest of the Lord.
The next set of phrases pronounce penalties upon Ammonihah. First, Alma tells them that their iniquity "provoketh" God. In other words, they have incurred his just wrath. God is not turning on them unjustly. Alma then speaks of two "provocations." The two provocations will lead to two destructions.
The first provocation is their current cultural rejection of the gospel. The Lord has warned them that they will be destroyed if they do not repent. When they do not repent, Ammonihah is destroyed according to the word of the Lord.
The second provocation is much more serious. While their unrepentance will lead to their temporal destruction, their unrepentance will also lead to a second destruction. This second will not just kill the body, it will be "the everlasting destruction of your souls."
[unto the last death, as well as the first.] The "last death" is the spiritual death, or the second death. The "first" is the temporal death. Alma indicates that both temporal and spiritual death await them. In this case, both come because of their unrepentant state.
Rhetorical: Alma has very nicely tied his entire sermon together at this point. He has described a temporal death, and a spiritual death. Now he makes both very personal by declaring that both of them imminently await the unrepentant people of Ammonihah.