I'm more struggling with the Hebrews verse that talks about if we keep on deliberately sinning, we somehow forfeit our sacrifice.
Ok. I am not sure if you saw the following section on the Website link I gave so I have cut an pasted it. It deals with that very issue.
Heb 9:27-28 Just as man is destined to die once, and after that to face judgment, so Christ was sacrificed once to take away the sins of many people;
So what did that just say, man dies once, so in like manner Jesus dies once. So from my rendering that is a life for a life, one life time of sins for one sacrifice. We don’t face judgment until after we die. A further verse that supports the idea that sin is covered for a life time is the following
1Jn 5:16 If any man see his brother sin a sin which is not unto death, he shall ask, and he shall give him life for them that sin not unto death. There is a sin unto death: I do not say that he shall pray for it.
Note that Paul says that any sin that is not taken to the grave is forgivable, we are just not to pray for peoples sins once they die. It means that if God has left us alive he is seeking eternal life for us, he wants us restored. We are to pray for life for the sinning believer while they live. It is only if you die in sin that it is too late.
How forgivable is sin, and once we receive the Holy Spirit are we a super being incapable of sinning? First we must go to a verse directed to those who HAD received the Holy Spirit and it says:
1Jn 1:7-9 But if we walk in the light, as he is in the light, we have fellowship with one another, and the blood of Jesus, his Son, purifies us from all sin. If we claim to be without sin, we deceive ourselves and the truth is not in us. If we confess our sins, he is faithful and just and will forgive us our sins and purify us from all unrighteousness.
So firstly he said “if we claim to be with out sin”, or the devil tells you were 100% with out sin, and have now stuffed up, we should quote that verse, “If we claim to be without sin, we deceive ourselves and the truth is not in us” but what else does it say God is “is faithful and just and will forgive”, and to forgive “all sin”. Faithfulness means a person sticks by us even when we don’t do the right thing. Justice is doing what is fair. God sees it as fair to forgive a person seeking repentance, to deny a person the right to forgiveness is unfair, but note God is both faithful and just. And furthermore what of the verse below:
1Jn 2:1-2 My dear children, I write this to you so that you will not sin. But if anybody does sin, we have one who speaks to the Father in our defense—Jesus Christ, the Righteous One. He is the atoning sacrifice for our sins, and not only for ours but also for the sins of the whole world.
But if anyone does sin, we have one who speaks in our defence, so Jesus is actually defending you. Note he is the sacrifice for “our sins”, not just the unbelievers sins. So a Christian can sin and be justified. Remember what Jesus said to his disciples when they asked how many times their brother could sin and still be forgiven.
Mat 18:21-22 Then Peter came to Jesus and asked, "Lord, how many times shall I forgive my brother when he sins against me? Up to seven times?" Jesus answered, "I tell you, not seven times, but seventy-seven times”.
The above verse means infinitely, all the time. When a brother in Christ wants repentance God said “forgive them”. God does the same with any sin he forgives when ever we ask.
And what about the book of James, referring to Christians who have gone back to sin:
Jas 5:19-20 My brothers, if one of you should wander from the truth and someone should bring him back, remember this: Whoever turns a sinner from the error of his way will save him from death and cover over a multitude of sins.
So if some one moves away from God, wanders into error, and sin they can be bought back to repentance. Also the bible says in Ezekiel
Eze 18:23 Have I any pleasure at all that the wicked should die? saith the Lord GOD: and not that he should return from his ways, and live?
Eze 18:31-32 Rid yourselves of all the offenses you have committed, and get a new heart and a new spirit. Why will you die, O house of Israel? For I take no pleasure in the death of anyone, declares the Sovereign LORD. Repent and live!
What God, does not delight in the death of anyone, so he is not delighting in sinners perishing. He says “Why will you die?”, there is no need to die, all we need to do is repent, change our thinking, and we will have life. Again he says:
2Pe 3:9 The Lord is not slow in keeping his promise, as some understand slowness. He is patient with you, not wanting anyone to perish, but everyone to come to repentance.
So if we confess our sin, it is pardonable, why well the sacrifice of Jesus is available today. Why well God is “faithful and just”, “not willing that anyone perish”, taking “no pleasure in the death of anyone”. But remember it is a life for a life, once for all sin, in the same way it is appointed for man to die once and face the judgment. Jesus death only paid for this life’s sins, if we don’t repent before we die, there is no sacrifice for eternal sin, Jesus died in the flesh, not the Spirit, he did not suffer hell for us, only death in the body. But hey don’t be scared if you are alive and reading this there is no problem. The only sin that will kill you is totally unrepentant sin, not willing to come back for forgiveness no matter what God says, and if you have that sort you are probably not even interested in reading this page. God is not unjust, he is faithful. Ask God to restore his relationship with you, and he will not cast you out. You will be saved. I will finish with a verse and an idea, the bible says:
Luke 11:13 If ye then, being evil, know how to give good gifts unto your children: how much more shall your heavenly Father give the Holy Spirit to them that ask him?
Just think for a moment, I am an earthly father and I have a son, do you think that if my son spoke something bad against me, or even said "I no longer want you as my father", would I cease to have compassion on him. I would certainly still love him. God says that he is kinder than us, more loving, not less loving. He even calls our love in comparison to his evil. The bible says "how much more", will the Father give the Holy Spirit to them that ask him. Ask God for his Spirit, and he will give it, he certainly won't deny you salvation based upon any decision you have made, it is His faithfulness and love that keeps us secure not our past.