What does Genesis 5:3 mean?

This verse begins a pattern repeated for the remainder of this chapter. In each of these verses, the next notable member of the generation is listed, along with his age when the next son of Noah's line was born, and his age when he died.

Adam was 130 when Seth was born. This verse connects to the previous two verses in noting that Adam fathered Seth in his own likeness and after his image. In this way, humans continue the pattern established by God when He made man in His own image. The likeness of God continues to be passed down from one generation to the next. The long lifespans described here would have also served another important purpose: keeping witnesses to history alive to personally teach future generations. Looking at numbers given in this chapter, we see that Seth dies only 14 years before the birth of Noah—an extraordinary preservation of the past for the human race prior to the flood.

As we have seen, Seth was not Adam's firstborn son. Both Cain and Abel were born, grew up, and began their professions before Cain murdered Abel. It is likely Adam and Eve had many, many other children before Seth was born as a replacement for the murdered Abel (Genesis 4:25). Seth's line, however, is the one that leads to Noah and, through him, to the rest of the human race as we know it today.