A question about the tribes of Isreal?

ive just recently red Isaiah, and Jeremiah through out this month and i was wondering why does God refer to some of his people as (For example) The House of Jacob, its confusing because i thought he would refer to them as there partiular tribe like his does when he says The House of Judah if im not mistaken judah is one of the 12 tribes. Sorry if im not clear with my question im kinda of confused, can some one help me out Thank you