what is revealed by Mr Campbell about house of shaws to David Balfour? What is the purpose of revealing this to David?

Mr. Campbell takes the occasion to tell David what he knows of his fortune. David's father had asked the minister to deliver to his son a letter after his death. With the letter, his sixteen year old son could travel to the house of Shaws, once home to his father. David is surprised since he never knew his poor father to be related to such a high family. The minister assures him that the relations are there and that he should hope to be received well by them. He nervously asks Mr. Campbell if he should go to which the minister replies quickly that he should.