"These are spots in your feasts of charity, when they feast with you, feeding themselves without fear: clouds they are without water, carried about of winds; trees whose fruit withereth, without fruit, twice dead, plucked up by the roots." (Jude 12)
We often speak of people who have been "born again" through faith in Christ as being "twice born" men or women. Jude, however, here speaks of certain people who are "twice dead." Such people already, Jude says, "were before of old ordained |or 'forewritten'| to this condemnation, ungodly men, turning the grace of our God into lasciviousness |or 'anarchy'|, and denying the only Lord God, and our Lord Jesus Christ" (Jude 4).
Apparently there are some people who, even while still living, have already been consigned to hell, and thus are not only "dead in trespasses and sins" (Ephesians 2:1, the innate condition of all men until they are born again), but twice dead, already participating in the second death. These are apostate teachers who have known and understood the gospel of the grace of Christ and have even for a time presented an outward appearance of teaching and believing biblical truth--perhaps even believing mentally that they had become disciples of Christ. But then they became apostates, repudiating true creationism and the doctrines of salvation by grace through the saving work of Christ their Creator, even though they had formerly taught these truths. "There remaineth no more sacrifice for sins" (Hebrews 10:26), and they are forever apostate.
This description of such teachers in Jude (vv. 4-19) is a searing condemnation of such deceivers, as well as a sober warning to any who might be tempted to heed their false teachings. Rather, Jude exhorts us to "earnestly contend for the faith" (Jude 3). HMM