When Sherem admitted he had been deceived by the devil, he feared lest he had committed “the unpardonable sin,” for he had lied unto God and had denied the Christ. Although it is not clear in the Book of Mormon whether or not Sherem was guilty of committing the unpardonable sin, the Lord has explained in other scriptures the characteristics of those who do commit this sin. In the Doctrine and Covenants, the Lord has said:
Thus saith the Lord concerning all those who know my power, and have been made partakers thereof, and suffered themselves through the power of the devil to be overcome, and to deny the truth and defy my power—They are they who are the sons of perdition, of whom I say that it had been better for them never to have been born;
For they are vessels of wrath, doomed to suffer the wrath of God, with the devil and his angels in eternity;
Concerning whom I have said there is no forgiveness in this world nor in the world to come—
Having denied the Holy Spirit after having received it, and having denied the Only Begotten Son of the Father, having crucified him unto themselves and put him to an open shame.
These are they who shall go away into the lake of fire and brimstone, with the devil and his angels—
And the only ones on whom the second death shall have any power. (D&C 76:31-37.)
Orson Pratt has explained the meaning of the term “second death,” which is used in this scripture and which comes upon the sons of perdition:
Second death, What is that? After you have been redeemed from the grave, and come into the presence of God, you will have to stand there to be judged; and if you have done evil, you will be banished everlastingly from His presence—body and spirit united together; this is what is called the second death. Why is it called the second death? Because the first is the dissolution of body and spirit, and the second is … a banishment—a becoming dead to the things of righteousness… . (Journal of Discourses, 1:288.)