The author of Hebrews here (Paul, in my estimation) does a masterful job in summarizing the wilderness experience of the children of Israel - all those who came out of Egypt. He has nothing positive to say about them. Not one word. His description of them - the whole generation - is about rebellion, testing and provoking God, going astray, doing evil, being unbelieving, having hard hearts, being deceitful, sinful, disobedient.
In what is essentially an epitaph on an entire generation of Israelites, Paul concludes that they were denied entrance into the Promised Land because they never believed God and that led to their disobedience. They simply did not take His Word as anything of value. So they did not believe it, did not put any stock into it, and did their own thing.
What we see, the end of it all was, as it says here in the New King James, their corpses fell in the wilderness. This is a particularly effective and picturesque illustration, that their corpses fell in the wilderness.
The King James makes it a little bit more macabre. It says it is their carcasses [that] fell in the wilderness. The Phillips version reads that they left their bones in the desert.
The Amplified Bible reads, whose dead bodies were scattered in the wilderness. The Good News Bible (we are getting a little bit more into paraphrases here) reads, who fell down dead in the desert. And, finally, the Message says that they ended up corpses in the wilderness.
The result of all their sin and their rebellion and their provoking God is that they left their rotting carcasses from one end of the wilderness to the other. Every single one of them died. Paul says, Indeed, was it not all who came out of Egypt, led by Moses? All! Every. Single. One.
Paul's exhortation here is very urgent, very sobering. Beware, lest you be like them, he says, as in the day of rebellion - when they hardened their hearts against God.
The stakes are so much higher for us! It was not just a matter of physical life being lost, or physical destruction; but once we are talking about spiritual Israel (spiritual matters), we are talking about eternal life at stake. If we express the same attitudes and actions as they did - with the knowledge and the calling that we have - the effect is so much worse. Hebrews 4:1 says that we should be terrified of falling short of God's Kingdom! Let us therefore fear of not entering into that rest, because if we do not, that is it.
This section says pretty much the same thing that Paul said in Hebrews 3 and 4. If you think you are doing okay, if you feel satisfied with your spiritual standing, if you feel like your relationship with God is okie dokie - watch out, because something is going to be coming. You have become self-satisfied. You have become like the Israelites who felt that their closeness with God (in the covenant) would take care of everything for them, and they could do pretty much as they pleased. So if we find ourselves falling into this sort of attitude, we will end up falling just as Israel fell. Their bad examples are inscribed in black and white in God's Word so that we can avoid repeating those things.
Now, because our hearts have been transformed by God's Spirit we do not have to follow that sinful destructive pattern of Israel. And as Peter writes,