This verse echoes back to the end of Genesis 5, where Noah's lineage was first introduced:
These are the records of the generations of Noah. Noah was a righteous man, blameless in his time; Noah walked with God. Noah became the father of three sons: Shem, Ham, and Japheth. (Genesis 6:9-10)Noah is the second man in Genesis who is said to have walked with God. Enoch, Noah's great-grandfather, also walked with God. While Noah only temporarily escaped death, Enoch totally escaped death: he was not, for God took him (Genesis 5:24).
Noah was not perfect. Jesus Christ is the only man who ever lived without sin. Scripture is clear that even the most righteous of men still sin: Indeed, there is not a righteous man on earth who continually does good and who never sins. (Ecclesiastes 7:20). Noah, like all others, was born in the image of fallen Adam (see Man in the Image of Man); he was not blameless because all of his actions in the first six hundred years of his life were perfect. Rather, he was blameless because God made Him blameless.
Not only was Noah blameless, but Noah was blameless in his time. Out of all the times in human history, Noah's time might have been one of the hardest times in all of history to live a righteous life. There wasn't, as in Elijah's time, seven thousand other men who had not bowed the knee to Baal (Romans 11:4). Noah and the seven others who boarded the ark were the righteous remnant— there wasn't anybody else... At the time that the flood hit, Noah and his family were the only lights still shining forth in a dark and twisted world.
As in Genesis 5:32, Noah's sons are once again listed: Shem, Ham, and Japheth. It may seem repetitive to continue mentioning these men, but it's important to recognize that these are the men who repopulated the entire earth after the flood. Every single man born after the flood can trace his lineage back to at least one of these three men.
The Pre-Flood World: Filled With Violence (Part 1) - Genesis 6:11-12
Noah's Name: Its Meaning and Significance - Genesis 5:29
Enoch: A Prophet in the Pre-Flood World - Genesis 5:21-24
Who Are the Sons of God? - Genesis 6:1-4
Righteous Men of the Pre-Flood World - Genesis 4:26