Genesis 5: 5: And all the days that Adam lived were nine hundred and thirty years: and he died.
Genesis 11: 10 – 11: These are the generations of Shem: Shem was an hundred years old, and begat Arphaxad two years after the flood: And Shem lived after he begat Arphaxad five hundred years, and begat sons and daughters.
A quick glance at Genesis 5 shows that before the Flood, the longevity of man was hundreds of years, whereas after the Flood, the longevity of man gradually decreased to its current threescore and ten (Psalm 90: 10). With this in mind, we come to a stark realization that for Adam to have had such an extensive lifespan of 930 years, then he must have been still alive to see the generations of offspring that came after him. And indeed, this is true, for Adam lived till the time of Lamech, who was the ninth generation that descended from him.
With such a long lifespan, Adam was able to share personally with his descendants what life was like in Eden before the Fall happened. He was able to tell about how he never aged, nor got sick or weary, of how he could travel at the speed of thought and create with the power of the Spoken Word, and of how he communed with God in the evening time. He could tell about the harmony that once existed among the animals, and he could tell about the Serpent, the Cherubim, the flaming Sword and so much more. Indeed, there were many tremendous insights Adam was able to share to the generations that came after him, and we can only imagine that they must have listened in silent awe to his tales of the paradisical world he once lived in and of how paradise was lost.
This ancient knowledge of the creation, of Eden, and of the Fall was able to reach Abraham’s son Isaac through two unique links in the genealogical chain of Adam. These two links were Methuselah and Shem, the eighth and eleventh generations from Adam. Methuselah is the oldest man on record in the Bible. He was born 243 years before Adam died, so he would have gotten to know Adam quite well in that time. Methuselah lived up to the year of the Flood and was able to tell Shem all that he had learned from Adam. Shem (who lived for 600 years) was born 98 years before Methuselah died, and lived up to the 60th year of Isaac. As Shem was the eleventh generation from Adam, so Isaac was the eleventh generation from Shem. Thus it was through Methuselah that highly accurate information was passed down from Adam, and was carried over the Flood through Shem, who could then relay it to Abraham and Isaac.