David was a man after God’s own heart and Abraham was a friend of God. No one can please God without being regenerated (Rom 8:8-11).And I would suggest to you that prior to the Cross and Pentecost not one man or woman was alive spiritually.
How could an unregenerate person be an author of Scripture? Surely if Moses and David and the prophets were unregenerated, then there would not have been any Scripture prior to the cross. Nor would there have been any men giving true prophecies. All revelation from God would have come from angels or directly from God—not through men.
Anna and Simeon clearly represent OT saints when they rejoiced to see the baby Jesus in the temple. There can be no doubt that they believed Jesus to be the Messiah, the Son of God. Yet according to John 6:47; 11:25-27; and 20:31, all who believe that have eternal life. Anna and Simeon and all OT believers believed in the coming Messiah for eternal life and hence they were born again.
Finally, the biggest problem with this view is that it makes OT believers unbelievers. Oh, they believed something. But they are not seen as believing in the Messiah for everlasting life. They are not seen as being sure that they are eternally secure by faith in the coming Messiah. As a result, two or more saving messages occur. If prior to Jesus’ baptism people were born again by believing something less than the truth that the Messiah guarantees eternal life to all who simply believe in Him, what is it they believed? And why, then, would Paul in Romans 4 and Galatians 3 use Abraham as an example of one who believed the same saving proposition we believe? If Abraham was born again simply because he believed God exists, then how could he be a model for how people are born-again today?
Old Testament believers were not spiritually dead. They were spiritually alive. True, only some were indwelt by the Holy Spirit and that indwelling was not permanent. But all OT believers were regenerated and all were sealed. To believe otherwise is to reduce OT believers to people who were not children of God, were not spiritually alive, had no ability to please God, and who had no current relationship with God.
All who believe that the Messiah guarantees everlasting life to all who simply believe in Him are regenerate people. Regeneration bridges every so-called "dispensation."
Acts 10:43 "To him (Christ) give all the prophets witness, that through his name whosoever believeth in him shall receive remission of sins."
The Old Testament Prophets preached Christ. And those Old Testament saints who believed were born again, made alive in Christ, and received remission of sins.