Introduction
Arphaxad is a son of Shem, named both in the Table of Nations of Genesis 10:22 and, more significantly, as the starting point of the more detailed genealogy given in Genesis 11:10-26, which traces the line from Shem through Arphaxad, Shelah, Eber, Peleg, Reu, Serug, Nahor and Terah down to Abraham, the line the rest of Genesis follows most closely.
Family
Two genealogical appearances
Arphaxad appears first in the broad, largely undeveloped Table of Nations of Genesis 10, listed simply as one of Shem's sons alongside Elam, Asshur, Lud and Aram. He then appears again as the opening figure of the more detailed, formally structured genealogy of Genesis 11:10-26, which gives ages and lifespans for each generation in a pattern similar to (though with shorter lifespans than) the earlier Sethite genealogy of Genesis 5, tracing the specific line that leads to Abraham and the patriarchal narrative that follows.
Significance
As the first name in the genealogy connecting Shem to Abraham, Arphaxad marks the structural transition in Genesis from the broad, universal scope of the Table of Nations to the narrower, more specific line of descent the text will follow for the remainder of the book.