"If we
deliberately go on sinning after we have received the knowledge of the truth, no further sacrifice for sins remains, but only a fearful expectation of judgment and of raging fire that will consume all adversaries."
First of all, Hebrews is referring to Hebrew/Israelite Christians.
We are saved by grace through faith. Therefore, faith is what keeps connected to God's grace. If a believer goes back to willfully living according to the sinful nature, he has turned away from the faith, being in a state of apostasy. If a believer remains in and dies in that state, then there is nothing else that can save him/her. Consider the following:
"My brothers and sisters, if one of you should wander from the truth and someone should bring that person back, remember this: Whoever turns a sinner from the error of their way will save them from death and cover over a multitude of sins."
First of all, James it is apparent by the words "My brothers and sisters" it is obvious that James is writing to Christians. And if one of those believers should wander from the truth, notice that in that wandered state, that they are accumulating sin and because of willful sin, death. If someone should turn that believer back to walking in faith, then those sins that he/she was accumulating will be covered over and that person saved from condemnation.
In further support of a believer being able to loss their salvation, I would refer you to the unforgiving servant, especially the last verse. It demonstrates that after that servant was forgiven, because he did forgive his fellow servant, that his debt that was forgiven was reinstated, thus verse 35.
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Because of this, the kingdom of heaven is like a king who wanted to settle accounts with his servants.
24As he began the settlements, a debtor was brought to him owing ten thousand talents.
25Since the man was unable to pay, the master ordered that he be sold to pay his debt, along with his wife and children and everything he owned.
26Then the servant fell on his knees before him. ‘Have patience with me,’ he begged, ‘and I will pay back everything.’
27His master had compassion on him, forgave his debt, and released him.
28But when that servant went out, he found one of his fellow servants who owed him a hundred denarii.
g He grabbed him and began to choke him, saying, ‘Pay back what you owe me.’
29So his fellow servant fell down and begged him, ‘Have patience with me, and I will pay you back.’
30But he refused. Instead, he went and had the man thrown into prison until he could pay his debt.
31When his fellow servants saw what had happened, they were greatly distressed, and they went and recounted all of this to their master.
32Then the master summoned him and declared, ‘You wicked servant! I forgave all your debt because you begged me.
33Shouldn’t you have had mercy on your fellow servant, just as I had on you?’
34In anger his master turned him over to the jailers to be tortured, until he should repay all that he owed.
35That is how My heavenly Father will treat each of you unless you forgive your brother from your heart.”
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