The word Enlightened (photizo from phos = light) means to bring to light, to shed light upon or to cause light to shine upon some object, in the sense of illuminating it. Figuratively, photizo means to give guidance or understanding, to make clear or to cause something to be known by revealing clearly. John 1:9 describes Jesus, the "true Light," giving light "to every man"; but this cannot mean the light of salvation, because not every man is saved. This light either leads to the complete acceptance of Jesus Christ or produces condemnation in those who reject such light. These Hebrews were exposed to the truth, but exposure to truth does not guarantee full acceptance and submission to the truth.
They had tasted of the heavenly gift, and in such a way as to give them a distinct impression of its character and quality, yet they still fell away. Inherent in the idea of tasting is the fact that one might or might not decide to accept the thing that is tasted. For example, the same Greek word (geuomai) is used in Matthew 27:34 to say that those crucifying Jesus "offered him wine to drink, mingled with gall; but when he tasted it, he would not drink it."
Partakers (metochos from metecho = have with, describing participation with another in common blessings) describes one who shares with someone else as an associate in an enterprise or undertaking. It speaks of those who are participators in something. Business partner, companion. Participating in. Accomplice in. Comrade. Metochos is used elsewhere in Hebrews in the context of believers (Hebrews 3:14 "For we have become partakers of Christ") and thus the statement that the readers have been made partakers of the Holy Spirit seems at first glance to be support that true believers are being addressed, yet there are other ministries of the Holy Spirit that precede the indwelling of believers. It is very plausible to envision an individual becoming a sharer in or partaker of the Spirit (and his pre-salvation ministry, convicting of sin, righteousness and judgment to come) by responding for a time to His drawing power intended to lead sinners to Christ. The translation "shared" implies something done in company with others and before salvation all believers shared in the convicting ministry of the Spirit Who drew them to salvation. Note also that the writer does not state that these individuals were indwelt by the Holy Spirit or sealed by the Holy Spirit or possessors of the Spirit's pledge (guarantee) of future inheritance. It sounds to me that these Hebrews, after knowing and being convinced of the truth, they willfully reject it. We can repent "change our mind" enough to be convicted of and know the truth, but if we reject it and there is no heart submission to this knowledge of the truth, then this would not be repentance unto life. Renew them once again unto salvation would be a definitive statement to prove that these Hebrews were saved and lost their salvation.
Greater evidence that these people were not saved is given in verse 9. Things change in this verse, for now He is speaking to those truly saved (calls them BELOVED). He says that even though he speaks like this concerning THOSE types of people, He is convinced of better things concerning YOU. Things that ACCOMPANY SALVATION. In Hebrews 6:7-8, we read - For the earth which drinks in the rain that often comes upon it, and bears herbs useful for those by whom it is cultivated, receives blessing from God; but if it bears thorns and briars, it is rejected and near to being cursed, whose end is to be burned. In this agricultural metaphor, those who receive final judgment are compared to land that bears no vegetation or useful fruit, but rather bears thorns and thistles. When we recall the other metaphors in Scripture where good fruit and fruitfulness is a sign of true spiritual life and bad fruit or a lack of fruit is a sign of those who are not saved (for example - Matthew 3:8-10; 7:15-20; 12:33-35), we already have an indication that the writer is speaking of people whose most trustworthy evidence of their spiritual condition (the fruit they bear) is negative, suggesting that the writer is talking about people who are not born again believers. Thorns and thistles and falling away does not accompany salvation.
As in Hebrews 10:26, we see - For if we sin willfully after we have received the knowledge of the truth, there no longer remains a sacrifice for sins. Just having the knowledge of the truth does not save a person if there is no heart submission to that knowledge. For this knowledge to be of any spiritual value, there must be a heart submission to that knowledge. When we get to verse 39, we see that these Hebrews draw back to perdition and did not believe to the saving of the soul. How can we say they were "saved" and "lost their salvation" when they "did not believe to the saving of the soul?"