Although Moses had written concerning the generations of Shem in the previous Chapter, he revisits the generations of Shem with a focus on Arphaxad.  The reasoning behind this revisit is to focus on the generations leading to Yeshua Messiah.  The genealogy follows Arphaxad’s grandson, Eber.  Scripture says that Eber had sons and daughters, however, the generations leading to Messiah goes through  Peleg who was the ancestor of Abraham.  Abraham’s extended family in Ur of the Chaldees is described prior to an in-depth treatment of Abraham’s life in subsequent Chapters.