"We speak what we know and testify what we have seen, and you do no believe our witness." Nicodemus came to Jesus by night. He is the only one that is taught about his need to be born from above. When Jesus cautions Nicodemus, the choice to believe or not to believe is put forth. Jesus, when He speaks, testifies to something which has existed since Genesis 3:15. The question is who are His disciples and from what generation do they come from?
In terms of when this occurs: without the Holy Spirit men are condemned to love the things of this world. Men will inevitably do the will of Satan. Jesus commands Paul, "...I now send you to open their eyes, in order to turn them from darkness to light, and FROM THE POWER OF SATAN to God..." Acts 26:17-18 God works the same always. In terms of Jesus' ministry while on earth, the future apostles received the Holy Spirit in John 20:22. In terms of Jesus' disciples before His ministry on earth we can see that Zacharias, Elizabeth, Simeon, and Anna are righteous before the Lord. If the Sciptures declare one righteous then God has enabled them to be so. Not just in words but in action. "For our gospel came not unto you in word only, but also in power, and in the Holy Ghost." 1 Thessalonians 1:5
All the saints who were santified by faith in Jesus are His disciples. The Father, Son, and Holy Spirit work as one.
"All were baptized into Moses in the cloud and in the sea, all ate the same SPIRITUAL DRINK. For they drank of that spiritual ROCK that followed them, AND THAT ROCK WAS CHRIST." 1 Corinthians 10:2-4 We know that most of them walked away from the Lord because they chose not to believe. Yet there was a remnant. Even in the time of Elijah, God reserved 7000 who did not bow their knee to Baal. If by grace then it is not of the law given on Mount Sinai. The law given on Mount Sinai condemned. No one is made perfect by the law. It only teaches about sin. This is why the there are two covenants coexisting. In reality all who do not call upon the Lord are condemned by the law of God's righteousness. There is a promise availabe to all who repent and follow God in faith. In Christ, God reconciled the world to Him.
"Rejoice, O Gentiles, with His people; For He will avenge the blood of His servants, and render vengeance to His adversaries; HE WILL PROVIDE ATONEMENT for His land and His people." Deut. 32:43 This work of God covers all generations who are the just who live by faith. You see only God can provide the atonement which brings salvation to His creation.