When the sinner dies before repenting, he has sealed his fate, literally. We can be sealed to the Lord and be brought to heaven or we can be sealed to Satan and taken to hell (Mosiah 5:15). This is just another instance in which Satan has copied the Lord's plan. Indeed, Satan's kingdom was created in the blurry image of God's. Hence, he has his own priesthood, he has his own angels, he has his secret combinations instead of sacred covenants, and he seals the sinner to himself. The result is truly frightful, for the devil hath all power over you.
Spencer W. Kimball
"There is a sad note of finality in that last statement. It matches the words of Samuel the Lamanite to those who would procrastinate the day of their salvation-'it is everlastingly too late, and your destruction is made sure' (Hel. 13:38); and it recalls those of Mormon relative to his wicked contemporaries-'the sorrowing of the damned.' (Morm. 2:13.)
"The key factor in such a situation is the withdrawal of the Lord's Spirit. In the final battle days of the Jaredites, 'the Spirit of the Lord had ceased striving with them, and Satan had full power over the hearts of the people' (Eth. 15:19.)" (The Miracle of Forgiveness, p. 118)