Coriantumr was told that the key to peace was his own repentance (Ether 13:21). As a leader, Coriantumr's individual disobedience became a key factor in the destruction of an entire nation. Now after two million casualties, Ether's memory finally quickens. But the violence has become a self-perpetuating monster, continually accelerating out of Coriantumr's control. The national consequences of his individual disobedience had become irrevocable. He had, in effect, procrastinated the day of his salvation until it was everlastingly too late (Hel 13:38).
Neal A. Maxwell
"This grizzled veteran began to reflect upon the loss of two million of his people, and there were the beginnings of sorrow. 'He began to repent of the evil which he had done; he began to remember the words which had been spoken by the mouth of all the prophets, and he saw them that they were fulfilled thus far, every whit; and his soul mourned and refused to be comforted.' (Ether 15:3.) But sorrow which is compelled only by casualty figures is not enough. Coriantumr's sorrow must have been the 'sorrowing of the damned' (Morm. 2:13), because he was still locked into a way of life from which he seemed unwilling to disengage fully." (Ensign, Aug. 1978, "Three Jaredites: Contrasting Contemporaries")