Regeneration (I believe, you don't have to if you don't want to) is by DIRECT OPERATION of the Holy Spirit. The Holy Spirit was in the days of Creation. Remember the Spirit of God moved over the waters ? as in Genesis 1:2 ?
And HOW did Abel knew what type of offering will be a sweet savor to, and accepted by, God ? The same way that Peter and coy recognized who they were that Jesus was conversing with on the mount of transfiguration, unless of course, there was a technology available to them that gave them an image of Moses and Elijah and these fishermen and carpenters of Jesus' time was, well, geeky.
And what did Jesus say to Peter when He blurted out, "you're the Christ, the Son of the Living God" ? Did Jesus say, "come on Peter, you guessed, but, never mind, you're right, you know".....No, He said, that His Father which is in Heaven, told him (Peter).
So, you're mistaken.
Old Testament saints were regenerate.
Their regeneration, then, as now, was by DIRECT operation of the Holy Spirit.
The real question is, "is ALL of Israel, regenerate ?", no.
Now, remember the old man at the temple they took Jesus to when He was a baby ?
How many years he has been waiting, seen babies come and go, yet recognized Jesus ?
Or how John the Baptist, as an unborn, leapt in Elizabeth's womb when Mary, with Jesus in her womb, spoke to her?
What am I saying, that the old man was regenerate, and so was John the Baptist.....in the womb ?
Yep.
Direct operation of the Holy Spirit.
No preacher, no gospel, no nothing from man.
Besides, you are referring to Israel, a NATIONAL people called by God as His people, as in, "tell Pharaoh, let MY PEOPLE go."
1) Yes, the Holy Spirit places individuals spiritually into Christ.
2) Yes, the Holy Spirit's "operation" is present in the Genesis creation.
3) Yes, Abel's offering was more pleasing to God. I am not aware of the verse that says the the HS inspired Abel to choose the more pleasing offering.
4) Yes, Peter was inspired with the knowledge Jesus was the Christ.
5) None of the above says the OT Saints had been made perfect, which occurs after a person is spiritually placed in Christ. (1 Peter 5:10)
6) The OT Saints who were inspired by the Holy Spirit were not first regenerated. If they had been been regenerated they would have gone to heaven when they died, but they did not.
7) Yes, man does not contribute to regeneration, it is accomplished by God.
8) No, I am not referring to National Israel, but to those who gained approval on the basis of faith. (Hebrews 11:2)