V.23 We are told to hold fast, and then we are reminded that, although we are weak, yet He is always faithful.
V.26-31 In spite of that one sacrifice and all its perfect value, there still was the danger that some might profess to be Christians, and later turn away entirely. For such, there was no hope, nothing left but punishment. These were never believers. Those who do not believe in eternal security, use these along with Hebrews 6:4-64For it is impossible for those who were once enlightened, and have tasted of the heavenly gift, and were made partakers of the Holy Ghost, 5And have tasted the good word of God, and the powers of the world to come, 6If 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. (Hebrews 6:4‑6) and 2 Peter 2:20-22 to try to prove that a person could be lost after having once been saved. (But see John 10:2828And I give unto them eternal life; and they shall never perish, neither shall any man pluck them out of my hand. (John 10:28)).
V.29 “Sanctified.” If a person turned from Jewish sacrifices, and took his place among Christians by profession, he was in that way set apart from those who were still religious Jews. He has the name of a “Christian.” If such a professor turns against the Christianity which he professed, see what words are spoken to such a man.
V.32-34 The marks of real believers in Christ.
V.39 There were many whose profession of faith in Christ was real.