What in the world does that mean, "Perfect in his generations?" Does it mean that socially, Noah's family was fit for polite society? That Noah had a good pedigree?
Yes and No. Polite society had nothing to do with the fact that Noah had a good pedigree--which he did. The answer to this question can be found in Genesis chapter 6 verses 2 and 4, where we are told that the sons of God took the daughters of men as wives and had children by them.
Noah was perfect in his generations because none of his ancestors nor his three sons had any traffic with "The Sons of God." No intermarriages between the sons of God and the daughters of men had taken place within his family tree.
Was this simply a cultural thing? Had national identities already begun to form within the relatively new human population?
It is commonly suggested that the "Sons of God" were descendents of Seth (as Noah was), and that the "Daughters of Men" were the descendents of Cain. There is no scriptural basis, however, for this line of reasoning.
Scripturally, we find that Adam was a son of God (Matthew 3:38). We find that angels, both fallen angels and holy angels, are called sons of God (Job 1:6). But from the fall of man until the birth, death and resurrection of Jesus Christ, we do not find another human besides Adam ever referred to as a "Son of God."
When Adam fell, he forfeited the right for his descendents to be called "Sons of God." That right was not restored until Jesus came and paid the penalty for Adam's sin. We read about this in John 1:12 where it says, "But as many as received him, to them gave he power to become the sons of God..."
After Adam sinned, not a single human had any power to be called a "son of God"--not even Noah, who was perfect in his generations and walked with God.
So who were these sons of God who took the daughters of men as wives and had children by them?
They were angels who defected from God. The very same ones who are presently imprisoned in Tartaras for leaving their first estate (1 Peter 3:19-20, Jude 6). These angels married the daughters of men and bore children who were quite magnificent. Magnificent...giant... bullies, according to the Word of God (check out the Hebrew).
Noah's family tree was not tainted by this unholy union between the daughters of Audawm (Adam) and the Ben Elohiym (sons of God) .
This was very important, because if it had been, then the prophecies concerning the Messiah would have become null and void. But God's Word always comes to pass, and God rescued Noah and his family. And Jesus, the Messiah, was born of their perfect lineage.
Because of that, those of us who call on his name to be saved are given power to become Sons of God.
Is there really any power we'd rather have?