Huh? You must've misunderstood me
The question being addressed in this conversation is: What is the difference from OT to NT, in how the Holy Spirit relates to believers?
It seems to me that you believe there isn't a difference. Yet clearly there is. What is that difference? All the things I said were examples of that difference.
Now maybe the confusion here is in the sematics of one being atoned for as opposed to being indwelt by the Spirit of God? Those on the OT side of the cross were atoned for in the same manner as those on the NT side are. The atonement actually took place outside of time (as well as inside of time); and this is why Jesus is the "lamb slain from the foundation of the world". (Revelation)
Yet there are clearly differences between the OT people who were atoned for and the NT post Pentecost believer. The most notable difference is in what they understand about redemption itself. Note too; OT people have no assurance of that redemption. And thus most likely the reason David made the statement about "Please don't take Your Spirit from me."
Besides the acknowledgement that David understands that on account of his sin, he does deserve judgement. Yet clearly he has no assurance of what we understand as having been atoned for to begin with. Keep in mind that we have a lot more "knowledge" than they had. And that I believe springs out of our having a far different experience with the Holy Ghost than they had.
Jesus said: "I will send the Comforter."
(Well, don't they have the Comforter now?) In what ever capacity the Holy Ghost is operating prior to Pentecost; apparently it's not a "comforter" role. Jesus wouldn't have to tell them that if they already had the same comforting experience of the presence of the Holy Spirit that Jesus himself had.
Jesus was God incarnated in human flesh; but also lived his life as "part of" the rest of the Trinity. The Father and Spirit were "in his world"; all of which was materially, physically, spiritually, psychologically and emotionally.
Jesus's experience of God was different than the experience of any of the disciples. And one could argue that is because Jesus had no sin; yet their experience of God changed after Pentecost; (and they remained sinners). Post Pentecost, hey now understand the Holy Ghost as a "comforter". They are also told they are given power from on high (to preach the gospel). Paul also talks about power to live a Godly life comes from the indwelling of the Holy Ghost.
Ezekiel 36:26 talks about receiving a new heart and a new spirit (Spirit). 2 Corinthians 3:3, Paul picks up on this heart of flesh reference from Ezekiel. Jesus tells Nicodemus "You must be born again." Jesus makes another reference that one must be born of water and spirit (Spirit). Paul makes several references to being a "new creature" / a "new man" etc.
We associate this kind of language with what we call "regeneration".
You say that you believe OT believers were "regenerated". And if they were "regenerated" in some format; it clearly was not in the same manner as we see in the NT. Keep in mind though too, that being regenerated is not the same thing as being atoned for.
In Luke 22:32 Jesus makes an interesting statement to Peter. He says "I've prayed for you that your faith not fail". (Some acknowledgment here that Peter "believes" / "has faith" in.... something.) Then Jesus says: "And when you are converted; strengthen your brethren." But wait a minute? Peter already "believes" though. (Jesus has just stated that Peter has faith of some sort.)
Now other passages where this word "converted" is used are clearly talking about what we would call "regeneration". (Matthew 13:15, Matthew 18:3, Mark 4:2, John 12:40, Acts 3:19, Acts 28:27)
So yes, OT believers exhibited some form of "faith". But we know redeeming faith is a gift from God. (Ephesians 2:8) And maybe here is the difference where "human faith" fails because of sin.
Example related to Peter is that he got scared and ran away when confronted by this servant girl, as to whether or not he knew Jesus. Peter who told Jesus that he would be crucified with Jesus. Peter is later crucified. Jesus does actually tell Peter that will happen. Yet note that even just before Jesus dies; he tells Peter "when you're converted..."
We know the law of God is written on the conscience of men. This is what makes people accountable for their sin. They are without excuse for they see God in the creation.
Now obviously trying to understand God without the written revelation of Scripture is difficult. But the question for those people is "Do you obey the witness that you have?" Paul says that those who are without the law; yet obey the law are a law unto themselves. How many of those people (who never got the opportunity to hear the gospel in the first place) are actually atoned for? Bit of a different subject here; but it still does address the question of how the Holy Spirit relates to people pre and post Pentecost.
In Revelation we see a great multitude of people of "every kindred, tribe, tongue and nation" appear in heaven out of what we commonly theologically call "the great tribulation". When did that actually happen becomes an "eschatological question" in our "last days".
The Scriptural evidence though points to, that this happened as part of the atonement. We see this because Jesus states that "no flesh would be saved" if the "great tribulation" wasn't "shortened". Well, if we believe that the atonement was completed at the cross and that there is no time now where salvation can be lost? That puts that event as part of the crucifixion.
Note the people who appear in heaven appear with the "lamb as was slain". This event actually took place upon the death of Christ. He ascended into heaven and took all those that he'd atoned for (out of hades) up with him at that point in history. So now when a believer dies; they ascend strait to heaven.
Why do I bring this up though?
Because in this passage we see (via "every kindred, tribe, tongue and nation") people who lived on earth who were never anywhere near OT revelation. We have Chinese and Africans, Europeans and Native Americans and all these people are Old Testament side of the cross. All clearly atoned for; yet subject to the paganism of their individual cultures.
Which again: What sort of relationship to the Holy Spirit did they have, that they obeyed the revelation that they had? (Which was what they could glean out of observing the creation and obeying their conscience.)
Does what I'm saying make more sense to you now?