This means that all the saints of the OT who trusted God and followed his ways in the obedience of faith were born again by the Spirit and indwelt by the Spirit. For example, Num 14:24 says of Caleb, "My servant Caleb, because he has a different Spirit and has followed me fully, I will bring into this land." And Num 27: 18 says, "And the Lord said to Moses, 'Take Joshua the son of Nun, in whom is the spirit, and lay your hand upon him.'" The OT believers were saved the same way we are: they were born of the Spirit, they trusted in God's promises, and they followed his commandments in the obedience of faith.
We can include the Psalm where David is repenting of his sin and cries out to God, Please don't take your Holy Spirit from me. Many of us were taught that the OT believers didn't have the dwelling of the Holy Spirit but the scriptures say otherwise.
We were separated from God until the atoning death of Christ. What ever help they had from God was not the indwelling of the Holy Spirit of God Himself.
I usually agree with what you say but I think maybe you are missing some very wonderful blessing, as I was, before I knew what the OT scriptures actually say instead of reading it with the eyes of my teachers.
The scriptures are clear that at least some of them in the OT who obeyed God in faith did have the Holy Spirit. Job said this...para.
I know my Redeemer lives and He will walk upon the earth someday and I will see Him.
Jesus said that He knew Abraham, the NT says it was Jesus who was with the people in the wilderness. When Moses saw the backside of God, who was that? It could only have been Jesus.
What about that we have the Holy Spirit indwelling in us? Isn't that new?
This is what I understand, not that I am correct but it is something to think about and investigate.
No I can't say that all of the believers in the OT had the indwelling of the Holy Spirit but we knew some did.
Or that we have the Word written on our hearts? Isn't that new?
Yes that is through the NC.
What about that we have the mind of Christ? Is that new?
I would say that having the mind of Christ is progressive awareness and obedience to the Holy Spirit and God's Word.
I think that we can say that some of the OT faithful did this very thing.
What about salvation by grace? Is that new?
Salvation has always been by the grace of God. There is no other way to be saved. This was a lesson learned by Job.
Can we also agree that the Old Covenant was for the Israelite's, not Gentiles. This was NOT an all inclusive to all men covenant. This was a covenant with God's chosen people.
Abraham, was a Gentile and so was Issac and Jacob was a Gentile by birth, but they were Hebrews. Jacob became the nation Israel with his sons. Not all the original Israelites were Hebrews, a mixed multitude came out of Egypt. So those 20 yrs. old and younger were not all of Hebrew parents. If someone says they are a Jew by birth they are saying they are of Hebrew descent.
So at that time the only way a Gentile could be become one of this group of God's chosen people, the Israelites, was to declare their faithfulness to the God of the Jews and obey their the Laws that were given at Mt Sinai and added to as time went by, like Ruth. A man had to be circumcised as well.
Now it is not that way. We become a member of the commonwealth of Israel by adoption through faith in the Jewish Messiah Jesus and receive the Holy Spirit just the same as the Jewish believers did and do.
So yes the NC is very different than the OC.