The great ages of Abraham’s ancestors represent an important enigma in Genesis. Adam died at the age of 930, Noah lived for 950 years, and Methuselah was 969 when the Flood occurred. Instead of simply accepting or rejecting these ages, it makes sense to ask what they contribute to the story.
One contribution is that because of these ages many generations may have known each other. Noah, for example, may have known the 18 generations between Enoch, Adam’s grandson, and Abraham. This means that the genealogies of Cain may have something in common with those of Seth, the son Eva had after Cain killed Abel. When we investigate whether the Enoch and Lamech refer to the same person in these genealogies, we come across several cases of extramarital relations and of endogamy and incest.
Another contribution is that when we count the ages for the first seven patriarchs –from Adam to Enoch–, we see they add up to a total of 5,879. This is one year less than 5,880, which is 7 times 7 times 120. However, the age for Enoch is 365, a figure that refers to the days in a year. Whereas in a normal year there are 365 days, in a leap year there are 366. And with this number we do reach 5,880. The average age of the first seven patriarchs is therefore 7 multiplied by 120.
Whereas the number 120 reminds us of God saying, "My spirit does not stay forever in man, because he is only flesh; let his days be 120 years " (Gn6: 3), the number 7 reminds us of the seven pairs of pure animals (only one of impure animals) that Noah was asked to take onto the ark (Gn7: 2). Since these animals later had to repopulate the earth, it is obvious that 'impure' refers to incest. If we reflect on how pure animals may have repopulated the earth, we see that these seven pairs represent seven male lineages and seven female lineages and that the most practical way to avoid inbreeding or incest would have been for each of the seven male lineages (or female) to 'cross' in each new generation with each of the seven female (or male) lineages. This would mean that seven generations later each male (or female) lineage crosses again with the same female (or male) lineage. Since God created (begat) Adam in His likeness, he and Enoch had something in common. That would explain why Enoch is special. Not only did he die at the age of 365 years, the number of days in a year, but Genesis also says of him: "Enoch walked with God, and disappeared because God took him." (Gn5: 24)
Genesis offers the ages for Abraham’s ancestors in two groups of ten: the first ten (from Adam to Noah) had their 'heirs' before the Great Flood and the last ten (from Shem to Abraham) after it. 10 plus 10 equals 20, and so does 7 (a number that symbolizes good luck) plus 13 (a number that symbolizes bad luck). And when we now count the ages for the last 13 patriarchs (from Methuselah to Abraham) we reach a total of 5,867, or 5,880 minus 13. These 13 years equal 1 per patriarch. However, 13 is also Ishmael's age when God offered Abraham his alliance and ordered all the men of his house to be circumcised*. We thus see that God not only has something in common with Enoch, but also with Abraham.
*It is from that moment on that the patriarchs no longer manage to prolong their lives.