Charles Ellicott Commentary Isaiah 48:1

"Hear ye this, O house of Jacob, who are called by the name of Israel, and are come forth out of the waters of Judah; who swear by the name of Jehovah, and make mention of the God of Israel, but not in truth, nor in righteousness" — Isaiah 48:1 (ASV)

Are come forth out of the waters of Judah. —The words limit the wider terms of Jacob and Israel to the Judæan exiles. For the phrase, compare ye that are of the fountains of Israel (Psalms 68:26). The ideal attributes of Israel, swearing by the name of Jehovah ... are emphasized in contrast with their actual state of hypocrisy and unrighteousness.