In chapter 16, Abinadi summarizes his message to King Noah and his priests. That message is: "repent now."
The gospel of Jesus Christ is about us changing our lives. If we only serve Him with our lips, then our lives mean nothing. We must be "doers of the word" (James 1:22-23).
If a man confesses he believes in Christ and accepts Him as his lord but then never truly repents of his sins, then he will not be "saved."
Verse 5 says, "Remember that he that persists in his own carnal nature, and goes on in the ways of sin and rebellion against God, remaineth in his fallen state."
The consequence of living a carnal life is "endless damnation." (Mosiah 16:11). Just as a dam stops the flow and progress of water, so too does a life of un-repented sin stop our spiritual progression. If we persist in our own carnal wills and "never call upon the Lord" then our spiritual progression ceases. Our options to choose what type of life we want to live become slim and we are limited to the point of damnation.
Abinadi counsels his audience again to "tremble and repent of [our] sins and remember that only in and through Christ can [we] be saved."
Abinadi thus closes his sermon to King Noah and his priests.
Alma the Elder
We do not know much about Alma the Elder's life before he became a priest of King Noah. We know from Mosiah 17:2 that he was a young man and that he was a descendant of Nephi. After Abinadi delivered his message, we know that Alma's soul was touched and that he witnessed first-hand the iniquity of King Noah and his people. He did not counsel King Noah to repent per se, but he implored the king that he would simply release Abinadi. This request enraged Noah and he cast Alma out and sent servants to kill him.
Alma escaped with his life and wrote all the words which Abinadi had spoken (Mosiah 17:4). Thus Abinadi's mission was fulfilled. He touched at least one soul (D&C 18:15) and that soul would go on to be the means of convincing many souls of their errors (D&C 18:16).
Seal His Testimony
After three days of deliberation, the priests convict Abinadi of blasphemy and sentence him to death unless he would recall his words.
Abinadi immediately tells them that he will not recall his words and that he would rather die than deny his testimony. He forcefully tells them, "If ye slay me ye will shed innocent blood, and this shall also stand as a testimony against you at the last day." (Mosiah 17:10).
King Noah must have felt the sting of these last words of Abinadi for he was about to release him out of fear. But the hardened priests appealed to the pride of the king and in an instant King Noah sealed his own fate by heeding his priests.
Abinadi is scourged almost to death before his flesh was set aflame and he was left to burn to death.
In his final breaths, Abinadi ends his words to King Noah and the people the same way he began his words to them … with a prophecy of what will come to them if they do not repent. Thus ended the life of a great prophet.
Everyone has a part to play in this great plan of salvation. As John Taylor has said, if a person does not do his duty, God will hold him responsible for those he could have saved had he done his duty. Imagine if Abinadi failed to do his duty. The entire plot of the Book of Mormon from Mosiah 16 on depends on if Abinadi did his duty or not. From Abinadi comes the repentance of Alma. From Alma comes the repentance of hundreds or thousands of Nephites. He later becomes the High Priest of the entire church. From him comes his son Alma who later becomes a powerful tool in the restoring apostate groups. From Alma the younger comes Helaman who led the 2000 Ammonites in battle. From Helaman comes Helaman who becomes chief judge. From him comes Nephi and Lehi who brought to pass a radical change in the Lehite society. From Nephi comes Nephi the apostle who lived to see the coming of Christ. Indeed, Abinadi fulfilled his duty and the fruits of his labors are many.