15 Oh, how merciful is our God! And now behold, since it has been as much as we could do to get our stains taken away from us, and our swords are made bright, let us hide them away that they may be kept bright, as a testimony to our God at the last day, or at the day that we shall be brought to stand before him to be judged, that we have not stained our swords in the blood of our brethren since he imparted his word unto us and has made us clean thereby.
The king emphasizes repeatedly how difficult the process of repentance was and his fear that if the people fall back to violence they will fall away from Christ.

 I don’t think he truly believed that they could never be forgiven for defending themselves. Or if he did, that was based on a converts somewhat limited understanding. But what he understood was that engaging in violence would be direct defiance of God’s will and that doing so would place them in Satan’s grasp.
And so they people decided to be willing to face death rather than fall back into sin. They knew that in losing their life they would ensure eternal life.

I admire the people of Anti-Nephi Lehi for their faith and courage and willingness to put it all on the line for Christ.