Hebrews 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 is a difficult verse.
It’s either difficult to understand or difficult to accept.
“For it is impossible” has only one meaning – it can’t happen!
But what is it that can’t happen?
It is evident from the context it is talking about those accepting Christ as Savior, although many commentators teach against this believing these only flirted with Christianity.
A keyword in the whole meaning is found in the word “tasted”. To taste is not to eat. You do not sit down at the table to just taste the food but to eat, consume, and to fellowship with those sitting with you. To taste is just to sample it.
Perhaps those “tasting” never really get involved with Christ, hence, the flirtation with Christianity
Then we come to “if they fall away”. They desert the effort, the church, and turn away from Christ, to return to a totally godless life of sin.
Regardless, I think the great meaning of this verse is that salvation only happens once for an individual because Christ only died once for sin.
He did not die two or three times for you because once was sufficient (Romans 6:10).
So either you can only be saved once and it is impossible for you to fall away OR you can only be saved once and if you fall away you can never be saved again.
I am one that does not believe in losing salvation. One that is truly saved would not turn back.
If it appears as if someone does get saved and fall away, then John gives an answer – 1 John 2:19
They went out from us, but they were not of us; for if they had been of us, they would have continued with us; but they went out that they might be made manifest, that none of them were of us.