Genesis 10:21
“Unto Shem also, the father of all the children of Eber, the brother of Japheth the elder, even to him were children born.”
KJV
Read in Genesis 10Meaning
Shem is introduced as ancestor of the children of Eber and as a brother of Japheth, opening the final major branch of the genealogy.
Read carefully
The wording about Japheth's age or sibling relation is translated differently because the Hebrew permits more than one grammatical reading; the genealogy's focus is Shem's line through Eber.
Reflection
The narrative returns from broad peoples and territories to a specific family line, showing how biblical genealogy moves between the universal and the particular.