Jude 1:12- "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;"
What does the statement of being twice dead mean here? If Christians are twice born, then the reference of being twice dead can only be referred to the unsaved who are portrayed here to be living life as they please because they are not saved. Many of those in that crowd are actually proponents of the heresy of works salvation- they teach salvation is by works yet they live a sinful life just like the Pharisees. There is the physical death, the spiritual death and the second death. Christians get born physically like everybody else and when they are saved, they are born spiritually.
Remember that the spiritual birth can never be undone by any means because it's God who is in charge (and He NEVER fails to chastise the Christian whenever they screw up, yup He has other means to punish sin) and the Christian can never depart from the faith as a result of the second birth (1 John 2:19). When they are dead, they only die once. The Bible speaks of the second death in Revelation 20:6, Revelation 20:14 and Revelation 21:8 that the Lake of Fire is the SECOND DEATH, that is died twice. This is not in support of the teaching of annihilation of the soul but rather, it's being "living dead" in the Lake of Fire.