When God spoke to Job, He gave him some considerations from creation that everyone should ponder about
Elohim had blessed the human beings He had created and allowed them to have children. That way A'dham became the father "of a son" in his own likeness, "after" his own image. We were not told this about Cain and Abel simply because the text did not wish to discuss them at length. In this chapter 5 Moses goes straight to the third son of Adam, Enosh. It is noted that from that time the people started to call upon the Name of Jehovah God.
The Bible opens with the story of the beginning of everything, presenting the six periods of development (six days of creation) and the final period of establishment or rest.