With the story of three brothers, first of all, Harry gets to know what the symbol he and his friends look for means. Then he would be able to recognize who is probably related to the tale and to sort out their relationship. Also, he might thus know where or from whom he can collect all these three hallows which might be needed for the fight between him and Voldemort. As Hermione said that she saw the symbol on Cedric's grave, they might be able to find out the mystery of his death.
Teacher's note: Yes, poor Cedric turned out to be a big Hollywood star (Robert Pattinson, if I'm not mistaken). I like how concise this post is, yet based on the compelling details of this short sequence, I long for a little more disclosure in this excellent post. Thank you, author, for being first to respond to "The Deathly Hallows."
--mike
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