In John 3:10, when Jesus asked Nicodemus, “Art thou a master of Israel, and knowest not these things?” What things is Jesus referring to? If He is referring to being born again, how could Nicodemus have known? Isn’t this the first time the phrase “born again” was used in history?
Obviously, Nicodemus could only have learned this from his studies of the Old Testament. Beginning in Genesis there are hints of redeemer who would reverse the damage Satan had done (Genesis 3:15). In Genesis 5, the Hebrew root words from which the names of the 10 patriarchs came spell out the gospel story. In Genesis 22 Abraham and Isaac acted out the story of the Father giving His only son as a sacrifice for sin. Then there were the animal sacrifices which began in Genesis and demonstrated that only the shedding of innocent blood can remedy our sin problem. The Hebrew names of the 12 signs of the zodiac tell the story of the redeemer. And there are many more throughout the Old Testament. Because of them, people knew what John the Baptist meant when he introduced Jesus as the Lamb of God who takes away the sins of the world (John 1:29).
The New Covenant was first introduced to Israel in Jeremiah 31:31-34. But I think the concept of being born again is clearest in Ezekiel 36:24-27 where God promised to give the Jews a new heart and a new spirit. Gaining a new heart and a new spirit literally requires a person to die and be born again.
These examples are clearer to us after the fact than they were to them before the fact. But Jesus said Nicodemus, being a teacher, should have understood. Later James said not many of us should presume to be teachers because teachers will be judged more harshly (James 3:1). Nicodemus is an example of that.