When we read chapter four of Genesis, we will notice two things.

..........................................After seeing Cain murdering his brother Abel, the result of his life is traced for just a little ways and ends in Lamech who was also a nurderer. Genesis 4:17-23

............................Then we are shown another man. The third son born to Adam and Eve, named Seth.
Genesis 4:24

.............In this line came Noah, Shem, Abraham, Jacob and then Jesus Himself.

.....This shows us God's working now with this line.