The only sins not covered by the atonemet are specifically those related to departing from Christ to pursue a works righteousness (Hebrews 6:5-6, Galations 5:2-3).
What is the alternative or opposite of pursuing righteous deeds?
Sin.
There is no other alternative.
So one is either saved by:
#1. God's grace + sin (or)
#2. God's grace + righteousness.
Granted, it is wrong to pursue "Works ALONE Salvationism" (that does not include God's grace). This is what Paul was condemning that you have taken out of context to justify a sin and still be saved type belief.
Jesus taught us that keeping His commandments was a part of eternal life:
For Jesus said: "...if thou wilt enter into life, keep the commandments." (Matthew 19:17).
The rich man replied: "which ones?" (Matthew 19:18).
Jesus said: "Thou shalt do no murder, Thou shalt not commit adultery, Thou shalt not steal, Thou shalt not bear false witness, Honour thy father and thy mother: and, Thou shalt love thy neighbour as thyself." (Matthew 19:18-19).
Here is another one that says the same thing in Luke 10:
A certain lawyer stood up, tempting Jesus,
The lawyer said: "Master, what shall I do to inherit eternal life?"
Jesus said: "What is written in the law? how readest thou?"
The lawyer said: "Thou shalt love the Lord thy God with all thy heart, and with all thy soul, and with all thy strength, and with all thy mind; and thy neighbour as thyself."
Jesus said: "Thou hast answered right: this do, and thou shalt live."
(See Luke 10:25-28).
Did Jesus say these following words to the lawyer?
"Wrong! You have to trust only in my sacrifice and not worry about sin so much."
No, He most certainly did not! Jesus said that he answered correctly and He told Him to do this and He will live.
As for Hebrews 6:5-6:
Hebrews 6:5-6 mentions nothing about falling away due to keeping the commandments as a part of everlasting life. We know that this was a requirement by the Lord Jesus Christ Himself as I have shown above in Matthew 19:17 and in Luke 10:25-28.
Hebrews 6:5-6 is dealing with those Messianic Jews who wanted to go back to the Jewish religion in order to avoid being persecuted for a while until the persecution passed whereby they would later then openly become Christians again. The context of Hebrews 6:4-6 is "departing from the living God" as mentioned in Hebrews 3:12. The context of Hebrews 3:12 was not to be deceived by the deceitfulness of sin whereby they would have a hard heart in departing from the living God.
Also, when you read Galatians 5:2-3, it is talking about Circumcision Salvationism. If you were to actually read more carefully Galatians 5:2 it says,
"Behold, I Paul say unto you, that if ye be circumcised, Christ shall profit you nothing." (Galatians 5:2).
You have to understand that certain Jews were trying to deceive Christians to be circumcised in order to be initially saved. Is circumcision something of the Old Testament Laws or the New Testament Laws? According to Genesis 17:14, it was a salvation issue not to be circumcised while under the Old Covenant. But seeing we are not under the Old Covenant, but a New Covenant (New Testament, or New Contract), circumcision is no longer a required command. In fact, these Jews (who were trying to deceive these Christians that Paul is writing to) were not even applying circumcision correctly (even according to the Old ways). They were wrongfully saying that a person had to first be circumcised to be saved when this was never the case. Under the OT: An OT saint first had to believe in God as their Savior to be saved and THEN they had to be circumcised (See Romans 4:9-12). So these Jews had the order all wrong even for the OT. But we are under a New Covenant, and circumcision is no longer a necessary requirement to the faith anymore. That was the Old Covenant. So this is why Paul says if you seek to be circumcised, Christ will profit you nothing because they were thinking they needed to FIRST be circumcised in order to be saved.
This problem was addressed at the Jerusalem counsel.
- Acts of the Apostles 15:1 says, “And certain men which came down from Judaea taught the brethren, and said, Except ye be circumcised after the manner of Moses, ye cannot be saved.”
- Acts of the Apostles 15:5 says, But there rose up certain of the sect of the Pharisees which believed, saying, That it was needful to circumcise them, and to command them to keep the law of Moses.”............................................................................................................................................
- Acts of the Apostles 15:24 says, “Forasmuch as we have heard, that certain which went out from us have troubled you with words, subverting your souls, saying, Ye must be circumcised, and keep the law: to whom we gave no such commandment:”
There is a long list of sins that require confession and repentance. Carmality itself is rarely seen as leading believers away from Christ and onto perdition.
Why don't you share that list here? Anyways, grievous sin is carnality or a thing of the flesh. Hebrews 3 says that the deceitfulness of sin can harden a person's heart in departing from the living God. Please read that chapter several times in prayer.
You said:
There was a point where the church was inundated with immorality, these people were seen as deadly dangerous in 2 Peter, Jude, Thyatira. These people don't just have petty immorality in their lives, they are consummed by the lusts of the flesh and never converted in the first place. Gnosticism was such a heresy.
2 Peter 2:14 says they cannot cease from sin. When I talk to Eternal Security folk, they most times will defend the fact that they can never overcome sin in this life. Many will say they are saved if they abide in unrepentant grievous sin because they believe King David was saved while he committed his sins of adultery and murder. Do you believe King David was saved while he committed his sins aof adultery and murder?