BBC: Genesis 5:1-5
This is the book of the generations of Adam. When God created man, he made him in the likeness of God. Male and female he created them, and he blessed them and named them Man when they were created. When Adam had lived 130 years, he fathered a son in his own likeness, after his image, and named him Seth. The days of Adam after he fathered Seth were 800 years; and he had other sons and daughters. Thus all the days that Adam lived were 930 years, and he died. - Genesis 5:1-5
This is already the second time the phrase "generations" has been used. The first was to describe the "heaven and earth" (Gen 2:4). Now it is being used to describe the lineage of man through Adam. Seth here is given the privilege of the first born. Cain's line was cut of when he departed from the presence of the Lord and is listed previously (Gen 4:16-22). This line is the line "of God" and will provide insight in how to interpret the the events before the flood (Gen 6:2).
*The Bible Blogging Commentary is a slow and simple treading of the Scriptures. No quotes from other theologians and no explicit Greek/Hebrew lessons.*