Hebrew 6:4-6
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.
This passage seems to put a dagger into the argument that a save person cannot ever be lost for it describes a person who was enlightened, tasted the heavenly gift, became partaker of the Holy Spirit, and tasted the good word of God and the powers of the age to come. To most of us, that sounds like a saved person, but as one reformed saint explained to me, these people were never saved in the first place. When I asked how he knew this, he replied, "Because they fell away."
I did not want to jump into the swirl of that circular argument so I let sleeping dogs lie. But I have thought about what he said for a long time. He was also a proponent of total depravity, often citing 1 Corinthians 2:14 in the King James Version of the Bible, "The natural man receiveth not the things of the Spirit of God: for they are foolishness unto him: neither can he know them, because they are spiritually discerned."
So we have two conflicting statements. When I combine his two arguments, I have a paradox. Either these people were saved and fell away from it, or they were never saved and yet were able to be enlightened, taste the heavenly gift, partake of the Holy Spirit, and taste the good word of God and the powers of the age to come, all of which seem to be denied possible to a lost person according to1 Corinthians 2:14.
Are the lost sinners who were able to understand spiritual things until they fell away, or were they saved saints until they chose to fall away? If they were lost sinners, what did they fall away from?
If John Calvin were here, I'd ask him. (If I had a fire proof suit to wear.)
They were “once enlightened”. This shows that they were once saved, for only believers are said to be enlightened, as we read in scripture
Ephesians 1: 18. The eyes of your understanding being enlightened; that ye may know what is the hope of his calling, and what the riches of the glory of his inheritance in the saints,”
And in the book of Hebrews we read,
Hebrews 10: 32. But call to remembrance the former days, in which, after ye were illuminated, ye endured a great fight of afflictions;”
Those who do not believe in Jesus are said to be in darkness, not light. Only those who believe in Jesus can come out of darkness and be enlightened, as Jesus said,
John 12: 46. I am come a light into the world, that whosoever believeth on me should not abide in darkness.”
And Paul said,
Ephesians 5: 8. For ye were sometimes darkness, but now are ye light in the Lord: walk as children of light:”
Only the children of God are called children of light (or enlightened),
1 Thessalonians 5: 5. Ye are all the children of light, and the children of the day: we are not of the night, nor of darkness.”
We read also,
2 Corinthians 4: 4. In whom the god of this world hath blinded the minds of them which believe not, lest the light of the glorious gospel of Christ, who is the image of God, should shine unto them.”
This shows that unbelievers are not enlightened in Christ.
Unbelievers are in darkness and do not see the light (or enlightened),
Ephesians 4: 18. Having the understanding darkened, being alienated from the life of God through the ignorance that is in them, because of the blindness of their heart:”
Finally, in Isaiah 8:20 we read about the wicked having no light, “if they speak not according to this word it is because there is no light in them”. So, it seems the wicked are said to be in darkness and not light and not enlightened in truth unless they are saved (born again).