The debate is here, some ways of explaining

I have an hard time understanding Hebrew 6:4-8 so I will talk about what it could mean.
People have debates on what these passages really mean. I will explain that these words could mean.
1) It refers to Christians losing their salvation.
2) It is a hypothetical argument to warn immature Hebrew Christians (Hebrews 5:11-14)  that they must progress to maturity (Hebrews 6:1)  or else experience divine discipline Hebrews (Hebrews 7-8).
3) It refers to professing Christians whose apostasy proves that their faith was not genuine (1 John 2:19).
This view sees chapters 3-4 as a warning based on the rebellion of the Jews in the desert.
As Isreal could not enter the promise land after spying out the land and tasting its fruit so the professing Hebrew Christians would not be able to repent if they adamantly turned against "the light" they had received. According to this view, such expressions as "shared in the Holy Spirit", and "enlightened" indicate that such a persons had come over the influence of God's pact blessings and had professed to turn from darkness to light but were in danger of a public and final rejection of Christ, proving they had never been regenerated (Hebrews 10:26-31).

Hebrews 6:4-8

⁴ It is impossible for those who have once been enlightened, who have tasted the heavenly gift, who have shared in the Holy Spirit, ⁵ who have tasted the goodness of the word of God and the powers of the coming age ⁶ and who have fallen away, to be brought back to repentance. To their loss they are crucifying the Son of God all over again and subjecting him to public disgrace. ⁷ Land that drinks in the rain often falling on it and that produces a crop useful to those for whom it is farmed receives the blessing of God. ⁸ But land that produces thorns and thistles is worthless and is in danger of being cursed. In the end it will be burned.