Glad to talk. We may have to go back and forth a few times to get it all ironed out, but stick with me and we'll discuss it as much as you want.
First things first, though it's a small item. It's almost certain that Paul didn't write Hebrews. The terminology and style are so completely different from his that almost no one anymore thinks it's Paul. But so you know, some scholars still argue that it was. That's just a tiny point, though, and doesn't have anything to do with what you're asking.
Secondly, one of the REAL issues at hand: Can we lose our salvation if we doubt and continue to fall into sin?
This is such an important question in so many people's minds when they read Hebrews that once I read through Hebrews taking careful notes to see if Hebrews ever talked about the permanence of salvation, and IT DOES!
6.19: We have this hope as an anchor for the soul, firm and secure.
7.25: Therefore He is able to save completely those who come to God through Him.
9.15: For this reason Christ is the mediator of a new covenant, that those who are called may receive the promised eternal inheritance.
10.14: ...because by one sacrifice he has made perfect forever those who are being made holy
10.22: ...let us draw near to God with a sincere heart in full assurance of faith...
12.23: To the church of the firstborn, whose names are written in heaven.
12.28: Therefore, since we are receiving a kingdom that cannot be shaken...
(2.1: the metaphor "lest we drift away" implies that a person is in peril of being carried downstream past a fixed landing place and so failing to gain its security.)
So it seems to me that that author believes that you cannot lose your salvation. So it seems. Let's look at your worrisome texts.
Heb. 2.1-4. First of all, there is HUGE debate about who the "we" is (v. 1). The choices are (1) the Jews/Hebrews, (2) humanity in general, or (3) believers/those who are saved. Most commentators think (3): believers.
"So that we don't drift away" is a verb that means "to flow by or past; to glide by; to slip away." It is also used figuratively to mean "be washed away; drift away." It comes from the word for the flowing of a river. (We're just trying to grasp what the author is saying.) Jesus has been revealed to us as God (chapter 1), so pay the utmost attention to all you've heard so that you don't flow away like a river. If he's writing to the Hebrews, it's a message to Jews to recognize and accept Jesus, so that they don't flow past and neglect to latch on. If the "we" is Christians, then I think he's saying that Jesus is the anchor for our lives. These verses don't seem to be about losing salvation, but rather about making sure that we recognize Jesus as the only truth path to it. "Drift away" in 2 seems to be parallel to "neglect" in 3. Those who do not accept Jesus will continue to drift down the river of unbelief.
Heb. 3.7-4.13: The "hardening" of 3.8 has to do with the unbelievers in and among the Israelites. The true Israelites didn't rebel, didn't have hardened hearts, and didn't test God. The "sinful, unbelieving heart" of 3.12 gives the same idea. I still think he's talking to Jews/Hebrews (that's who the "brothers" of 3.12 seem to be). He's making a plea to his Jewish network to turn to Jesus and not be like the Israelites of old who refused to accept God's revelation of Himself.
Heb. 6.4-8: One of the toughest passages, but looking at it as a discussion of Christian maturity/immaturity misses the whole point. The author's point is not moral or spiritual dullness that needs a refresher course, but the superiority of the new covenant over the old one. Verses 4-6 are the crux for this discussion. The audience is not in danger of apostasy, rather in danger of exchanging the perfected teaching from the new covenant about Jesus in favor of the old covenant. (He then talks about Abraham and Melchizedek, neither of whom were under the law, the Mosaic covenant.) The plea seems to be, once again, that his Jewish friends find salvation in Jesus and not by the works of the old covenant.
Heb. 10.26-31: We can see the old covenant all through this text. Judaism had long distinguished between intentional and unintentional sin (Num. 15.29-31; Lev. 4.2, 22). The sin in this context is willful, unrepentant, thorough apostasy. The key phrase is in 26, "after we have received the knowledge of the truth." It's tough to know whether this person has received through hearing and subsequently rejected or received Christ into his heart. Verse 26 seems to indicate the latter, as do v. 29 ("sanctified") and v. 32 ("after you had received the light"). This is a very difficult text. Sanctification is a process, not an event. At the moment of salvation we are positionally sanctified (1 Cor. 6.11), during life we are sanctified progressively through our experiences (1 Pet. 1.5-7), but we are not ultimately sanctified until we are in the presence of Jesus himself after death (1 Jn. 3.2). It seems that it's not possible to fall away from Christ and lose your salvation, but if you openly and willfully reject Jesus you can repudiate your salvation (look also at 2 Tim. 2.11-13). Maybe this is what Hebrews is talking about here. This also possibly goes along with what Jesus said in the Parable of the Soils (Mt. 13.18-23).
Heb. 12.25-29: This again seems to be reinforcing his previous point that Jesus is the key and we dare not ignore or try to go around Him. If you're looking for salvation, Jesus is the Man.
We can talk about any of these more. They are very deep, and are even worthy of more conversation, if you wish. I happen to believe that Hebrews teaches that we cannot lose our salvation, though I guess that it might be possible to give it away. The difference is between an accident and on purpose. I believe Hebrews teaches you can just drift away, and oh no, I've lost what I had. No. But if you come to a place where you hate Jesus and you want nothing to do with Him, and you deliberately reject Him, He may just let you.
So there's no need to be frightened. Even your shortcomings cannot separate you from the love of God (Rom. 8.38-39). If you are aware of falling into sin, take action as the Bible teaches and repent—make it right. If we seek God, he will forgive and accept us despite our sin. We need not be afraid. Those who need to be afraid are those who come to a hatred of God (Mk. 3.28-2-9; Heb. 2.3; 10.31).
Talk to me some more. I'm sure you have more questions and conversation.