Genesis 10:21 - Joseph Benson’s Commentary on the Old and New Testaments

Unto Shem, &c. The word Shem signifies a name; but two titles are also added whereby to distinguish him: 1st, He was the father of all the children of Eber. Eber was his great-grandson; but why should he be called the father of all his children, rather than of all Arphaxad's or Salah's? Probably because Abraham and his seed, from Eber, were called Hebrews. Eber himself, we may suppose, was a man eminent for religion in a time of general apostacy; and the holy tongue being commonly called from him the Hebrew, was retained in his family in the confusion of Babel, as a special token of God's favour to him. 2d, He is styled the brother of Japheth, perhaps to signify the union of the Gentiles and Jews in the church.