From “Growing in the character of a disciple”: Chapter 2 – A closer look at how God develops us as disciples
The letter to the Hebrews seems to make it clear that it is possible for a Christian, even a real one, to fall so far, and to become so apostate, that there is no way back for them. It would appear that such a person may then end up being judged as an unbeliever at the Great White Throne instead of being judged as a believer at the Judgment Seat of Christ. In other words, it seems that an apostate can lose their salvation and end up being condemned:
4 For it is impossible to restore again to repentance those who have once been enlightened, who have tasted the heavenly gift, and have become partakers of the Holy Spirit, 5 and have tasted the goodness of the word of God and the powers of the age to come, 6 if they then commit apostasy, since they crucify the Son of God on their own account and hold him up to contempt. 7 For land which has drunk the rain that often falls upon it, and brings forth vegetation useful to those for whose sake it is cultivated, receives a blessing from God. 8 But if it bears thorns and thistles, it is worthless and near to being cursed; its end is to be burned.Hebrews 6:4-8 (RSV)
This next passage deals with the situation of a person who has believed the gospel, and begun to be a disciple and to become sanctified. It indicates that he is in a worse position than an outright unbeliever if he then falls away and ‘spurns the Son of God’. What else can that mean, other than that he must end up in the Lake of Fire? That is where every unsaved person will end up. But how can a person be saved and yet be in a worse position than someone who is in the Lake of Fire?
26 For if we sin deliberately after receiving the knowledge of the truth, there no longer remains a sacrifice for sins, 27 but a fearful prospect of judgment, and a fury of fire which will consume the adversaries. 28 A man who has violated the law of Moses dies without mercy at the testimony of two or three witnesses. 29 How much worse punishment do you think will be deserved by the man who has spurned the Son of God, and profaned the blood of the covenant by which he was sanctified, and outraged the Spirit of grace? 30 For we know him who said, “Vengeance is mine, I will repay.” And again, “The Lord will judge his people.” 31 It is a fearful thing to fall into the hands of the living God.Hebrews 10:26-31 (RSV)