Genesis 6:3

And the LORD said, My spirit shall not always strive with man, for that he also is flesh: yet his days shall be an hundred and twenty years.

1. The LORD's spirit strives or works hard with people.
2. The LORD's spirit has a limited amount of time to work with each individual, because they grow old and die.
3. The maximum life expectancy of human beings will drop from just under 1000 years to 120 years.
4. The LORD obviously said this to someone - otherwise, it wouldn't have been recorded, but who that was is not stated.
5. The LORD gives advance notice of things that will happen, and also provides explanations of how He works with mankind.
6. Despite the fact that we die, we appear to be worth a considerable investment of effort by the LORD's spirit while we are alive.
7. I'm uncertain what the phrase, "for that he also is flesh," means. My best guess is that it refers to the dual nature of human beings - a spirit enclosed by a body of flesh, the latter having a maximum lifespan of about 120 years.