“And Yahweh said: ‘My spirit won’t stay in man forever, since they’re also flesh; and their days shall be a 120 years’” (Gen 6:3).
The author of this text, the Yahwist, has Yahweh utter these words on account of the growing corruption on the face of the earth—the intermingling of the sons of god(s) and the daughters of man (6:1-4). Furthermore, the J source holds true to its portrait of an ever degenerating human life-span. From this point forward, no one lives longer than 120 years in the Yahwist source. Thus J concludes its Genesis narrative by mentioning that Joseph died at 110 years of age, and its Pentateuchal narrative by mentioning that Moses lived to 120 years (Deut 34:7).
P’s genealogical lists, however, display no knowledge of J’s claim, or outright dismisses it. For in the P textual tradition, Noah lives 950 years (Gen 9:29), Shem 600 years, Arpachshad 438, Shelah 433, Eber 473, Peleg, 239, Reu 239, Serug 230, Nahor 148, Terah 205 (Gen 11:10-32), Sarah, 127 (Gen 23:1), Abraham 175 (Gen 25:7), Isaac 140 (Gen 35:28), and Jacob 147 years (Gen 47:28). All these life-spans come from the Priestly composition. Again, we see the influence of Mesopotamian antediluvian kings’ list on the Priestly writer.
It is additionally possible to see, as noted in earlier posts, that P might be engaged in rewriting J’s narrative. Here, the issue for P may not be J’s 120 year limit on man’s life, but the reason behind it: man’s increasingly corrupt nature. In other words, the Yahwist decrees lesser life spans on account of man’s increasing sinfulness. So a decline in morality is expressed as a concomitant decline in mortality. By expressing continued longevity in man’s supra-human life spans, the Priestly writer on the other hand seems to be subverting yet again J’s negative portrait of mankind.