Chapter seven of 1 Chronicles is the second time in the book reference is made to the tribes that made up the Northern Kingdom of Israel. For the most part, Chronicles ignores the Northern Kingdom, but the writer does not mean to exclude them altogether.
In the first place, Chronicles is written after the exile of Judah in Babylon.
In the second place, the Northern Kingdom has been dissolved and exiled for nearly two hundred years. Would they not have disappeared altogether as a people?
Third, God promised that His people would be reunited again (see Ezekiel 37) – people of the north and people of the south.
And so, as the genealogy is presented, the writer wants his first readers to know that God’s people have not been lost. They are still around. We know where they lived, he says, and we know where they ought to live. The writer of Chronicles wants to unite the returning exiles around the need for trusting in God, submitting to the Davidic kingship (the only legitimate one presented in Chronicles), and uniting as God’s people.
It is a very Christian message. Trust in God. Submit to the King (Jesus). Love one another. Any other path leads only to exile – as Israel now knows.