In Mosiah 12:32 we have the priests declaring that salvation comes through the law of Moses, which they declare that the preach. The priests would therefore presume that they were saved, and Abinadi makes it clear that their belief that they are living the law of Moses will not only not save them, but their actions in the way they live that law (the denial of the atoning Messiah) will actually condemn them.
Mosiah 15:28
28 And now I say unto you that the time shall come that the salvation of the Lord shall be declared to every nation, kindred, tongue, and people.
Mosiah 15:29
29 Yea, Lord, thy watchmen shall lift up their voice; with the voice together shall they sing; for they shall see eye to eye, when the Lord shall bring again Zion.
Mosiah 15:30
30 Break forth into joy, sing together, ye waste places of Jerusalem; for the Lord hath comforted his people, he hath redeemed Jerusalem.
Mosiah 15:31
31 The Lord hath made bare his holy arm in the eyes of all the nations; and all the ends of the earth shall see the salvation of our God.
Rhetorical: To this point Abinadi still had not answered the implicit questions of the final three verses of Isaiah 52 that were posed to him as a question. He is now prepared to answer that part. With the salvation of mankind as the backdrop, Abinadi interprets the joy of Zion as the salvation that has come through the atoning Messiah. He sets this interpretation up in verse 28, and them simply repeats the verses. In his context, they now become self-evident. Abinadi will not deal with most of these verses directly, but does extract the phrase "see eye to eye" from verse 29 to form the basis of his concluding declaration which comes in our chapter 16.
Textual: The 1830 edition does not break a chapter here, and indeed, the break here awkwardly divides Abinadi's discourse from his conclusion. Chapter 16 should be read with Chapter 15.