For it is impossible for those who were once enlightened, and have tasted of the heavenly gift, and were made partakers of the Holy Ghost, And have tasted the good word of God, and the powers of the world to come, If they shall fall away, to renew them again unto repentance; seeing they crucify to themselves the Son of God afresh, and put him to an open shame.
Those people were aware of all that was involved in believing but didn’t themselves inwardly accept that belief. Thus having been fully made aware of what was available they rejected it and turned their backs on it.
It seems to go way beyond the word "believers" and there is nothing simple about it. They have five attributes and then "fall away (παραπίπτω)." It is so serious "it is impossible" "to renew them again unto repentance." Now go look up Strong's "μέτοχος" for "partaker" and mediate on it, if you will.
I think you meant “meditate” but anyway.
The Greek μετόχους or metochous meaning partakers.
Metochous - a sharer, partner, associate
Now let’s look at the indwelling of the Holy Spirit as is the case of a true believer.
Acts 2:4 And they were all filled with the Holy Ghost, and began to speak with other tongues, as the Spirit gave them utterance.
They received and were filled with the Holy Spirit.
John 20:22 And when he had said this, he breathed on them, and saith unto them, Receive (lambanó) ye the Holy Ghost:
Greek lambanó - Definition: (a) I receive, get, (b) I take, lay hold of.
Totally different words. In Hebrews 6:4 those who turned away had not “received” the Holy Spirit as a true believe does.
That’s what a “meditation” or “study” of the word shows.