I think it is in reference to those who don't stay faithful to the end.
Hbr 10:23 Let us hold fast the profession of [our] faith without wavering; (for he [is] faithful that promised;)
Hbr 10:24 And let us consider one another to provoke unto love and to good works:
Hbr 10:25 Not forsaking the assembling of ourselves together, as the manner of some [is]; but exhorting [one another]: and so much the more, as ye see the day approaching.
Hbr 10:26 ¶ For if we sin wilfully after that we have received the knowledge of the truth, there remaineth no more sacrifice for sins,
Hbr 10:27 But a certain fearful looking for of judgment and fiery indignation, which shall devour the adversaries.
Hbr 10:28 He that despised Moses' law died without mercy under two or three witnesses:
Hbr 10:29 Of how much sorer punishment, suppose ye, shall he be thought worthy, who hath trodden under foot the Son of God, and hath counted the blood of the covenant, wherewith he was sanctified, an unholy thing, and hath done despite unto the Spirit of grace?
Hbr 10:30 For we know him that hath said, Vengeance [belongeth] unto me, I will recompense, saith the Lord. And again, The Lord shall judge his people.
Hbr 10:31 [It is] a fearful thing to fall into the hands of the living God.
Gal 5:1 ¶ Stand fast therefore in the liberty wherewith Christ hath made us free, and be not entangled again with the yoke of bondage.
Gal 5:2 Behold, I Paul say unto you, that if ye be circumcised, Christ shall profit you nothing.
Gal 5:3 For I testify again to every man that is circumcised, that he is a debtor to do the whole law.
Gal 5:4 Christ is become of no effect unto you, whosoever of you are justified by the law; ye are fallen from grace.
Hbr 6:4 For [it is] impossible for those who were once enlightened, and have tasted of the heavenly gift, and were made partakers of the Holy Ghost,
Hbr 6:5 And have tasted the good word of God, and the powers of the world to come,
Hbr 6:6 If they shall fall away, to renew them again unto repentance; seeing they crucify to themselves the Son of God afresh, and put [him] to an open shame.
Hbr 6:7 For the earth which drinketh in the rain that cometh oft upon it, and bringeth forth herbs meet for them by whom it is dressed, receiveth blessing from God:
Hbr 6:8 But that which beareth thorns and briers [is] rejected, and [is] nigh unto cursing; whose end [is] to be burned.
2Pe 2:20 For if after they have escaped the pollutions of the world through the knowledge of the Lord and Saviour Jesus Christ, they are again entangled therein, and overcome, the latter end is worse with them than the beginning.
2Pe 2:21 For it had been better for them not to have known the way of righteousness, than, after they have known [it], to turn from the holy commandment delivered unto them.
2Pe 2:22 But it is happened unto them according to the true proverb, The dog [is] turned to his own vomit again; and the sow that was washed to her wallowing in the mire.