Ok Christ4Me, this is a common interpretation many go with on these Chapters. I once subscribed to it myself, but no longer. It doesn't fit the context.
The problem here is this: If Hebrews 3 and 4 is a teaching on salvation, the parallel he is running is inconsistent with other uses of the Wilderness analogy used in the NT. Their salvation was not compared to entering the promised land but rather to being delivered out of Egypt, and how some lost that salvation when they turned back to sin.
4 For certain men have crept in unnoticed, who long ago were marked out for this condemnation, ungodly men, who turn the grace of our God into lewdness and deny the only Lord God and our Lord Jesus Christ. 5 But I want to remind you, though you once knew this, that the Lord, having saved the people out of the land of Egypt, afterward destroyed those who did not believe. (Jude 1:4-5)
And as quoted already, Paul also related our salvation to being delivered out of Egypt, having been "baptized" into Christ, and "eating" of His body and "drinking" from Him as their spiritual Rock:
10 Moreover, brethren, I do not want you to be unaware that all our fathers were under the cloud, all passed through the sea, 2 all were baptized into Moses in the cloud and in the sea, 3 all ate the same spiritual food, 4 and all drank the same spiritual drink. For they drank of that spiritual Rock that followed them, and that Rock was Christ. 5 But with most of them God was not well pleased, for their bodies were scattered in the wilderness. 6 Now these things became our examples, to the intent that we should not lust after evil things as they also lusted. 7 And do not become idolaters as were some of them. As it is written, “The people sat down to eat and drink, and rose up to play.” 8 Nor let us commit sexual immorality, as some of them did, and in one day twenty-three thousand fell; 9 nor let us tempt Christ, as some of them also tempted, and were destroyed by serpents; 10 nor complain, as some of them also complained, and were destroyed by the destroyer. 11 Now all these things happened to them as examples, and they were written for our admonition, upon whom the ends of the ages have come. 12 Therefore let him who thinks he stands take heed lest he fall.
This is the same point Hebrews 3:7-9 makes in discussing the provocation, when he states, "7 Therefore, as the Holy Spirit says: “Today, if you will hear His voice, 8 Do not harden your hearts as in the provocation, in the day of trial in the wilderness, 9 where your fathers tested Me, tried Me, and saw My works forty years." Because they turned back from Christ who was their salvation, he then went on to state, "10 Therefore I was angry with that generation, and said, ‘They always go astray in their heart, and they have not known My ways.’ 11 So I swore in My wrath they shall not enter My rest.’”
So you see then that salvation was not the issue here - LOSS of salvation maybe, but had already been saved out of Egypt. The references to "entering into His rest" were to entering into the promised land of Heaven and the kingdom of God when all was said and done, and as already stated, the millennial rest of a thousand years peace is when that kingdom will be established upon the earth.