How is it that the atoning Messiah publishes peace? He redeems his people. This is such an essential act that were it not to be performed mankind "must have perished." The priests cannot claim salvation through the law of Moses. Regardless of the law, without the atonement there would be no salvation. In this Abinadi is reiterating his point begun in Mosiah 12:31 where he asks the priests if they believe that salvation comes through the law of Moses (and they answer affirmatively in verse 32). Abinadi has thus nailed that point to the priests condemnation. They have said they believe that salvation can come through the law, and Abinadi is boldly declaring that there is no salvation for anyone without the atonement of the Messiah, even with the law of Moses.