Jamieson, Fausset and Brown on Genesis 6:3

3. flesh--utterly, hopelessly debased.

And the Lord said, My spirit shall not always strive--Christ, as God, had by His Spirit inspiring Enoch, Noah, and perhaps other prophets (1Pe 3:20; 2Pe 2:5; Jude 14), preached repentance to the antediluvians; but they were incorrigible.

yet his days shall be an hundred and twenty years--It is probable that the corruption of the world, which had now reached its height, had been long and gradually increasing, and this idea receives support from the long respite granted.