New Defender's Study Bible Notes
5:15 an ancient nation. The Babylonian nation which would soon descend upon Judah was indeed the most ancient of all nations. It was at Babel that Nimrod established mankind’s first post-Flood rebellion and built the first post-Flood city (Genesis 10:10; 11:4).
5:15 O house of Israel. Note that God still recognized the southern kingdom (Judah and Benjamin) as Israel, even though the northern ten tribes (commonly called “Israel” to distinguish them from the southern kingdom) had already been carried away.
5:15 language. It was also at Babel that God transmuted the primeval language (probably preserved by Noah and Shem and eventually Eber and Abraham) into the Sumerian language and many others (Genesis 11:9).