SCRIPTURE Revelation 21:7–8 “He that overcometh shall inherit all things; and I will be his God, and he shall be my son.  But the fearful, and unbelieving, and the abominable, and murderers, and whoremongers, and sorcerers, and idolaters, and all liars, shall have their part in the lake which burneth with fire and brimstone: which is the second death.”  

COMMENTARY Christians must overcome the temptations of the world, and those that do will remain sons of God.  Those who exercise their free will to do evil, whether they claim to believe or not, will participate in the second death, which is spiritual death.  Not exactly the doctrine of guaranteed, unconditional eternal security.