I never say our own works save us. It is of faith and continuing in the faith grounded and settled and when we are not moved away from the hope of the gospel. This can happen if we harden our hearts to Gods leading and work and an evil heart of unbelief separates us from God.
The writer of hebrews is very very clear about this. He simply uses the Ot example as a scriptural reference for them.
"11 Let us labour therefore to enter into that rest, lest any man fall after the same example of unbelief."
That rest in Christ is now and future. But as the rest we are in now by faith , we need to continue in it or we can depart from God through unbelief. Its not a one time thing where you believe and then you can never fall. The writer says he and the other holy brethren can fall through unbelief.
This labour we are in is to sow to the spirit and yield to the Spirit ongoing to reap everlasting life. If we sow to the spirit we shall reap everlasting life. Even though now as all believers are in Christ and he is everlasting life, ( in him is life) we must abide (remain in him through continual faith and holding our confidence steadfast unto the end). This is how we eternally are partakers of Christ. Yes we are now and shall be as we continue in the faith unto the end
Alright, since you can't seem to grasp the meaning of this in Hebrews, let's step outside to a greater authority:
From John 6:
Then said they unto him, What shall we do, that we might work the works of God?
29 Jesus answered and said unto them,
This is the work of God, that ye believe on him whom he hath sent.
30 They said therefore unto him, What sign shewest thou then, that we may see, and believe thee? what dost thou work?
31 Our fathers did eat manna in the desert; as it is written, He gave them bread from heaven to eat.
32 Then Jesus said unto them, Verily, verily, I say unto you, Moses gave you not that bread from heaven; but my Father giveth you the true bread from heaven.
33 For the bread of God is he which cometh down from heaven, and giveth life unto the world.
34 Then said they unto him, Lord, evermore give us this bread.
35 And Jesus said unto them, I am the bread of life: he that cometh to me shall never hunger; and
he that believeth on me shall never thirst.
36 But
I said unto you, That ye also have seen me, and believe not.
37 All that the Father giveth me shall come to me; and
him that cometh to me I will in no wise cast out.
38 For I came down from heaven, not to do mine own will, but the will of him that sent me.
39 And this is the Father's will which hath sent me, that
of all which he hath given me I should lose nothing, but should raise it up again at the last day.
40 And this is the will of him that sent me, that
every one which seeth the Son, and believeth on him, may have everlasting life: and I will raise him up at the last day.
41 The Jews then murmured at him, because he said, I am the bread which came down from heaven.
42 And they said, Is not this Jesus, the son of Joseph, whose father and mother we know? how is it then that he saith, I came down from heaven?
43 Jesus therefore answered and said unto them, Murmur not among yourselves.
44 No man can come to me, except the Father which hath sent me draw him: and I will raise him up at the last day.
45 It is written in the prophets, And they shall be all taught of God. Every man therefore that hath heard, and hath learned of the Father, cometh unto me.
46 Not that any man hath seen the Father, save he which is of God, he hath seen the Father.
47 Verily, verily, I say unto you,
He that believeth on me hath everlasting life.
48 I am that bread of life.
49 Your fathers did eat manna in the wilderness, and are dead.
50 This is the bread which cometh down from heaven, that a man may eat thereof, and not die.
51 I am the living bread which came down from heaven: if any man eat of this bread, he shall live for ever: and the bread that I will give is my flesh, which I will give for the life of the world.
52 The Jews therefore strove among themselves, saying, How can this man give us his flesh to eat?
53 Then Jesus said unto them, Verily, verily, I say unto you, Except ye eat the flesh of the Son of man, and drink his blood, ye have no life in you.
54 Whoso eateth my flesh, and drinketh my blood, hath eternal life; and I will raise him up at the last day.
55 For my flesh is meat indeed, and my blood is drink indeed.
56 He that eateth my flesh, and drinketh my blood, dwelleth in me, and I in him.
57 As the living Father hath sent me, and I live by the Father: so he that eateth me, even he shall live by me.
58 This is that bread which came down from heaven: not as your fathers did eat manna, and are dead: he that eateth of this bread shall live for ever.
59 These things said he in the synagogue, as he taught in Capernaum.
60 Many therefore of his disciples, when they had heard this, said, This is an hard saying; who can hear it?
61 When Jesus knew in himself that his disciples murmured at it, he said unto them, Doth this offend you?
62 What and if ye shall see the Son of man ascend up where he was before?
63 It is the spirit that quickeneth; the flesh profiteth nothing: the words that I speak unto you, they are spirit, and they are life.
64
But there are some of you that believe not. For Jesus knew from the beginning who they were that believed not, and who should betray him.
Jesus says it again and again. Whoever
believes in Him will have everlasting life. But some - even some of His 'followers' - did not
believe. When the authors of the epistles in the NT wrote to churches, they were aware that there would be those in the churches who did not believe, but unlike Jesus, they didn't know beforehand who those with evil hearts of unbelief were.
If you can 'believe' and then 'unbelieve', this would be a lie because people could 'believe' but ultimately not come to everlasting life. This is also why Jesus tells the parable of the weeds. The enemy in the parable sows weeds among the grain, and the master of the fields chooses not to have his servants pull any weeds till the crop is grown because then they might pull some of the good crop by accident. These letters are written this way because the apostles and the writers of these epistles didn't know which were the good crop and which were the weeds, so they challenged everyone to inspect his own work and to challenge his own faith.