The correct answer to this open question is the following.
The situation does Beowulf discovers upon his arrival at Herot is that the terrible monster Grendel is causing so much destruction, horror, and pain to the people of Herot. There, King Hrothgar is an old man who has no power and health to confront the terrible monster that is devouring people and destroying property.
That is why Beowulf prepares an attack and marches to Herot to fight the monster. Beowulf is a man of integrity that has the character and strength to confront the monster. Beowulf wants to support King Hrothgar and to express his gratitude because in the bast, the King had helped Beowulf's family.