Rhetorical: Abinadi is picking up on a theme that he began and interrupted (see Mosiah 12:34-36). He has already cited this particular commandment, but stopped his citation of scripture at that point and began his discussion of how they were not teaching that particular commandment. Now he repeats it, along with the rest of the basic commandments listed in Exodus. Why?
Abinadi is condemning Noah and his priests. He has a message to deliver from God, and will not stop until he has delivered it. What is that message? As Abinadi's discourse develops it becomes clear that his message is the Messiah. The art of Abinadi's discourse is the way in which he turns the situation in which he finds himself into an occasion to deliver the essential message, which is the mission of Jesus Christ.
The approach he takes to this message continues to confirm the hypothesis about the nature of this new religious order that has been instituted by Noah. The priests declare that they are teaching the law of Moses, and that salvation comes through the law of Moses. That Abinadi must preach the Messiah to them clearly indicates that they have rejected that part of the religion they brought with them from Zarahemla (and the land of Nephi not all that long before). The priests are basically teaching the religion that Sherem proposed to Jacob, and Mosaic law without the Messianic understandings that had come to the Nephite prophets. It is an ancient law, and an interpretation that accepts it while denying modern revelation (modern to them).
Abinadi breaks the discourse at the command to have no other God(s) before Him because that is the crux of his message. The Noahites are believing in the wrong God, despite claiming to believe in the law of Moses. Abinadi picks up with the rest of the Exodus commandments because he will now deal with the entirety of the Law to show how the understanding of the priests does not match the reality of God. Of course the law of Moses is more than just the particulars that Abinadi cites, but these laws create the moral basis of the law, and it is a proper departure point for the argument that Abinadi is building.
Translation: Whether or not Abinadi is reading may be in question, but the comparison of the two citations Abinadi makes of this verse suggest that the translation process rendered them differently. In the citation found in Mosiah 12:36 the translation leaves out the conjunctive phrase "that is". It is returned in this verse, but becomes "which are," on the agreement with the plural "things" which is singular in both Exodus and Mosiah 12:36.
The sense of the verse is not changed, but the slight change of singular to plural with the resulting change from "that is" to "which are" would appear to be an indication of the oral translation/dictation method rather than a specific change in the underlying text. It is also impossible to know whether or not this change happened when Joseph translated, or when Oliver hear and wrote. There are clear indications that Oliver did hear incorrectly, and then made a change, so this may be a scribal error on Oliver's part (see Skousen, Royal. "How Joseph Smith Translated the Book of Mormon; Evidence from the Original Manuscript." In: Journal of Book of Mormon Studies. FARMS 1998, Volume 7, number 1, p. 25).