Charles Ellicott Commentary Genesis 6:9

"These are the generations of Noah. Noah was a righteous man, [and] perfect in his generations: Noah walked with God." — Genesis 6:9 (ASV)

THE GENERATIONS OF NOAH (Genesis 6:9; Genesis 9:28).

Noah was a just man and perfect in his generations. —“Just” is, literally, righteous, one whose actions were sufficiently upright to exempt him from the punishment inflicted upon the rest of mankind. “Perfect” means sound, healthy, and conveys no idea of sinlessness. It corresponds to the Latin integer, from which our word “integrity” is derived, and not to perfectus.

Generations (dôrôth) is not the same word as at the beginning of the verse (tôldôth), but simply means his contemporaries. And he was this because—

Noah walked with God. —See Note on Genesis 5:22.