Why is the death of Aeschere so important?

After Grendel's mother's attack on Heorot in which she kills Hrothgar's "rune-reader" and "shoulder-companion," Aeschere, Hrothgar greets Beowulf, who has yet to learn of the tragedy, with the angry comment, "Don't you ask about joy!" In the face of Aeschere's death at the hands of Grendel's mother, Hrothgar's celebratory tone of the previous night shifts to one almost of recrimination against Beowulf—even though no one could have expected an attack from yet another monster. From Hrothgar's perspective, he has lost not only a critical adviser but also perhaps his only skilled "rune-reader," the man who can cast and read those symbolic pieces of wood or bone that help guide Hrothgar and his people to success in peace and war. Beowulf, realizing the depths of Hrothgar's despair in losing his closest adviser and trusted warrior, becomes the counselor when he tells Hrothgar not "to sorrow, wise man," reminding him that Aeschere has already achieved fame in life. This is a moment when the roles between Hrothgar and Beowulf are, in a sense, reversed, and Beowulf takes the lead in their meeting. More important for Beowulf and his own fame, Beowulf recognizes that Aeschere's death requires an immediate—and successful—attack on Grendel's mother.