It seems they were considering a return to Judaism, which apostasy would prove their faith was not genuine (1 Jn 2:19),I'll jump in here...
Hebrew 6 starts off with..."Therefore"....so as the preachers say, we need to find out what the therefore is there for.
So we can go back to chapter 5....and you can probably apply your comment there.
And this is the whole purpose of the book of (Hebrews), to warn them not to go back but to go on with Christ. To not go on with Christ is to neglect the salvation He has given.
As well as not maturing in the faith.
It is my belief...take...that those of chapter 6 were truly believes and it isn't salvation in question but rather "blessings".
and would deny them entrance into salvation (by faith), just as Israel could not enter the promised land after spying out the region and tasting its fruit.
This chapter has often been identified with Moses and those wandering in the desert...not allowed to go into the promised land and receive the blessing.
If you're into Chuck Missler...he has a video on the chapter.