The reason of this return to the genealogy of the Benjamites seems to be the desire to connect the genealogical introduction with the historical body of the work. As the history is to begin with Saul, the genealogical portion is made to end with an account of the family of this Benjamite monarch.
Related Commentaries of 1 Chronicles 8:1
1 Chronicles 8:1
1 Now Benjamin begat Bela his firstborn, Ashbel the second, and Aharah the third,