Genesis 6: 1 - 7

 ¹And it came to pass, when men began to multiply on the face of the earth, and daughters were born unto them,
 ²That the sons of God saw the daughters of men that they were fair; and they took them wives of all which they chose.
 ³And 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.
 ⁴There were giants in the earth in those days; and also after that, when the sons of God came in unto the daughters of men, and they bare children to them, the same became mighty men which were of old, men of renown.
 ⁵And God saw that the wickedness of man was great in the earth, and that every imagination of the thoughts of his heart was only evil continually.
 ⁶And it repented the LORD that he had made man on the earth, and it grieved him at his heart.
 ⁷And the LORD said, I will destroy man whom I have created from the face of the earth; both man, and beast, and the creeping thing, and the fowls of the air; for it repenteth me that I have made them.

 We are now told about how people were progressing on earth and the answer is, not too well. These verses are found challenging by many people. It starts by saying how humans multiplied and how the "sons of God" liked our women and had children with them. We don't know who the "sons of God" were; but, it is generally believed to be fallen angels. It appears that fallen angels (demons) interbred with humans creating a new being. We do know that God was not happy about people interbreading with these fallen angels and we also know that, that is the reason he caused the flood to kill everyone.

Something interesting is that once people interbred with these fallen angels, everything they did and thought was evil. We are not to share space with spirits, it tells us that later in the bible; but, the world's experience with them has never been good.

One interesting thing said by God at this time was that he would not "strive" with humans forever. God has to strive with us to show us how to be with one another. He is not talking about striving with us as between him and us, he created us and could have eliminated us all. Instead he gives man a lifespan of 120 years and it has been the maximum age of people ever since.

We are told how people are living longer today; but, we are not. The average age has risen; but, the drop dead length has not changed. There were people living to be 100 over a thousand years ago. But, the bible tells us that we don't ever die, that seems contradictory. We die to this world and this flesh, we remain eternally spiritual, our essence, our thoughts, our unique take on the world, that which makes us, us, our soul our uniqueness.

What we are being told is that our time on earth is limited, we should remain true to being human and that he will not strive with us forever. Some can choose to have a deep relationship with him and remain with him or we can choose to be separate from him; but, this is the life in which you get to make that decision.