Jacob is describing the sons of Perdition. The context of verse 3 shows that the topic is those who are cast out into their own place—or in other words, those who are the sons of Perdition. The key reason why an individual is worthy of such a punishment is because they choose to deny the Holy Ghost. As the Lord said:
'Wherefore I say unto you, All manner of sin and blasphemy shall be forgiven unto men: but the blasphemy against the Holy Ghost shall not be forgiven unto men.
And whosoever speaketh a word against the Son of man, it shall be forgiven him: but whosoever speaketh against the Holy Ghost, it shall not be forgiven him, neither in this world, neither in the world to come.' (Matt 12:31-32)
The language of this chapter is reminiscent of the language used in DC 76 to describe the sons of Perdition. To make a mock of the great plan of redemption is similar to the phrase in DC 76, having denied the Only Begotten Son of the Father, having crucified him unto themselves and put him to an open shame (DC 76:35). Both phrases describe a disdain for the great atoning sacrifice of Jesus Christ. The reward for both groups is the lake of fire and brimstone.