If you read your bible more, perhaps you would have noticed these verses;
12 Neither by the blood of goats and calves, but by his own blood he entered in once into the holy place,
having obtained eternal redemption for us.
Done deal,,,,Having obtained... On the cross Jesus said It is finished.
Sorry, but you need to clarify that God said a lot of things that it is given to His people in eternal possession, but there was always a condition:
"IF YOU YOURSELVES DO NOT DEPART FROM MY COMMANDMENTS."
So there is only the promise that the Lord nothing is taken away and the other to choose not to be able to, but we lose it will be able to:
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12 take heed, brethren, lest there be in any of you an evil heart of unbelief, so that you do not depart from the living God.
13 But instruct one another every day, as long as it is possible to say, `Now,' so that none of you will be hardened by being deceived by sin.
14 For we have become partakers of Christ, if we only keep the life we have begun firmly to the end,
15 As long as it is said, ' Now, when you hear His voice, do not harden your hearts, as in the time of murmuring.'
16 For some of those who heard it murmured, but not all those who came out of Egypt with Moses.
17 But who did he resent for forty years?
18 Against whom did he swear that they would not enter into his rest, if not against the disobedient?
19 So we see that they could not enter because of their unbelief.
(Heb. 3: 12-19)
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1 Therefore let us be wary, lest, while the promise remains to enter into his rest, any of you should be found late.
2 For it was announced to us, as it was to them; but the word that was heard did not profit them, because it was not dissolved by the faith of those who heard it.
3 But we who believe enter into the rest, because He said, 'I swore in my anger that they would not enter into my rest,' even though His works were done in the beginning of the world.
4 For there is no place where it is said of the seventh day: and God rested on the seventh day from all his works.
5 And again here, ' They shall not enter into my rest.'
6 it still remains that some must enter therein, and they to whom it was first preached entered not in because of unbelief,
7 else defines a certain day, `today', saying through David after so long a time; as it is said: `today, if you hear His voice, harden not your hearts'.
(Heb.4:1-7)
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So here we see that "some did not enter" not because they were simply not pre-elected, but because they were not submissive and rejected the Truth themselves