Joseph Fielding Smith
"It is possible for people to get so far in the dark through rebellion and wickedness that the spirit of repentance leaves them. It is a gift of God, and they get beyond the power of repentance. How well Mormon speaks of that, in reference to the people who turned away with their eyes open, who turned against the truth some 200 years following the coming of Christ. The people rebelled; Mormon speaks about them and their condition beyond the power of redemption because of their wickedness and the hardness of their hearts, which the Spirit of the Lord could not penetrate.
"They sinned wilfully, and therefore salvation cannot come to them. It was offered to them, and they would not have it. They rejected it. They fought it and preferred to take the course of rebellion; and the Lord on one occasion said to Mormon, 'You shall not preach to these people; they have turned against me and you shall not preach to them.' He had a right to say that. Now why did he say that? Because they had every opportunity and would not receive the truth. They mocked at it, and so the Lord said, 'You don't have to talk to them; there is no need to cry repentance to them any longer.' And after a while Mormon still pleaded with the Lord to let him try again. It was useless." (Doctrines of Salvation, 2:195)