Q: Looking for a good understanding of Gen. 6:3. Mentions 120 years, yet they lived 500-700- years then–seems contradictory.
Gen. 6:3– Then the Lord said, “My Spirit shall not abide in man forever, for he is flesh: his days shall be 120 years.” -ESV
A: The “shall be” in the passage indicates that in the ‘future’ the lifespan will be 120 years.
After the flood, it did gradually shorten to that; and eventually to far less.
Life spans seem to be increasing with the event of modern medicine. I have read that scientists think that in the future and under the best of conditions, 120 may be attainable, but will probably be the limit- just like the scripture confirms.