Hebrews 6:4-9 reads as follows: (v4)  "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, (v5) And have tasted the good word of God, and the powers of the world to come, (v6)  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. (v7) 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: (v8)  But that which beareth thorns and briers is rejected, and is nigh unto cursing; whose end is to be burned. (v9) But, beloved, we are persuaded better things of you, and things that accompany salvation, though we thus speak."

Does this passage affirm you cannot or can fall from grace? Let's see what it teaches:

FIRST: Even though the Hebrew writer says these were "once enlightened", had "tasted the heavenly gift", had "become partakers of the Holy Spirit", had "tasted the good word of God", and had "fallen away", the Presbyterians insist that they were never saved!  That perverts the text. How could the Hebrew writer say they had "fallen away" if they were not saved?

SECOND: Verse 9 is not canceling out what was just said about those who had fallen away, but now addresses those among them who were still saved since they had not left the Lord: "I am convinced of better things concerning you, yes, things that accompany salvation."

THIRD: Remember that Hebrews is a warning to Christians not to fall away:  "Take heed, brethren, lest there be in any of you an evil heart of unbelief, in departing from the living God. But exhort one another daily, while it is called To day; lest any of you be hardened through the deceitfulness of sin. For we are made partakers of Christ, if we hold the beginning of our confidence stedfast unto the end"  (Hebrews 3:12-14).