So you believe that people who were saved before Pentecost were unregenerate?
That is very interesting, but I can hardly think it is correct.
'Now if anyone does not have the Spirit of Christ, he is not his' (Romans 8:9). Nicodemus was told before Pentecost that unless he was born again, he could neither see nor enter the kingdom of God. Why? Because
'That which is born of the flesh is flesh and that which is born of the Spirit is spirit' (John 3:6). When Peter confessed Jesus as the Messiah, he was told,
'.....flesh and blood has not revealed this to you but My Father who is in heaven' (Matt. 16:17; cf. 1 Cor. 12:3).
If you want to know how the New Covenant differs from the Mosaic Covenant, I listed elsewhere 17 ways in which it is better. I can post that again if it will be helpful. No doubt the Holy Spirit was poured out in greater effusion at Pentecost than hitherto, but that is not the gist of the New Covenant. Under the Old Covenant, membership was restricted almost entirely to the Israelites, and while people came into that covenant at birth, only a few were actually saved (Isaiah 1:9), the vast majority being unregenerate. The blessings of the New Covenant come to all people- that is, Jew and Gentile, male and female etc. (Joel 2:28). Everyone in the New Covenant knows the Lord (Jer. 31:34).
There has only ever been one way of salvation- by grace, through faith in Christ, whether looking forward or looking back. That is why Abel was a prophet (Luke 11:50-51), and why he still speaks today to those who will listen (Heb. 11:4). What does he say?
'Believe on the Lord Jesus Christ and you will be saved!'
You might care to read this:
https://marprelate.wordpress.com/2009/08/28/the-prophet-abel/