Heb 6:4-6, 4 For it is impossible, in the case of those who have once been enlightened, who have tasted the heavenly gift, and have shared in the Holy Spirit, 5 and have tasted the goodness of the word of God and the powers of the age to come, 6 and then have fallen away, to restore them again to repentance, …
A debate frequently arises in Christian circles if a believer can lose their salvation, meaning fall away, backslide. These verses for one have been employed to make a case of the possibility. I believe the writer of Hebrews is providing us with distinct words to consider, “enlightened” and ”taste”. To be enlightened is to be well informed or to be familiar with the knowledge, to “possess it” is completely different. Think of this, if you have the knowledge or tasted a mango, it does not mean you ate it. David in Psa 34:8 writes, “Oh, taste and see that the LORD is good; Blessed is the man who trusts in Him!”. He opens with “taste”, then transitions to “trust”. Note that the person he calls blessed is one that has both tasted and trusted, it’s a picture someone who has gone from engagement to marriage.
These are the kind of people Hebrews 6 is addressing. They have been enlightened, they have tasted, they like king Agrippa almost persuaded to become Christians but never were. A true believer can, may or will fall, the difference, he is not falling away. To fall is to offend God; to fall away is to abandon God. To fall is guilt; to fall away is apostasy.