So where exactly does it say that believers can be thrown into the lake of fire? If you want to play this game of throwing random Bible verses around, then I can play this game too, but how about we play it with clear verses in which there is absolutely no ambiguity of what it is saying? How about that?
For if, after they have escaped the pollutions of the world through the knowledge of the Lord and Savior Jesus Christ, they are again entangled in them and overcome, the latter end is worse for them than the beginning. For it would have been better for them not to have known the way of righteousness, than having known it, to turn from the holy commandment delivered to them. But it has happened to them according to the true proverb: "A DOG RETURNS TO HIS OWN VOMIT," and, "a sow, having washed, to her wallowing in the mire." (NKJV, 2Pe 2:20-22)
A person can be saved, then get entangled in sin, if they stay in it they will be lost.
For it is impossible for those who were once enlightened, and have tasted the heavenly gift, and have become partakers of the Holy Spirit, and have tasted the good word of God and the powers of the age to come, if they fall away, to renew them again to repentance, since they crucify again for themselves the Son of God, and put Him to an open shame. (NKJV, Hebrews 6:4-6)
A person who wanders into sin after having been enlightened, and a partaker of the Holy Spirit, can be lost if they die in their sins. There is no sacrifice once one dies in sin.