Beowolf's Heroic Aura?

At the beginning of Beowulf it tells of how Grendel (a demon descended from Cain) is terrorizing the people of Danes and after twelve years Hrothgar is powerless to stop him and yadayada Grendel now controls Heorot. Hearing of what has happened Beowulf decides to take the challenge and rides to help this noble cause. As he approaches Hrothgar's kingdom he and his men are stopped and questioned by a watchmen. The watchmen demands Beowulf tell him his business. Beowulf explains that he is there with his many armored soldiers to help fight Grendel. This shows to me that Beowulf must have an aura that he puts of that makes those he speaks to believe he is there for for a noble and heroic cause. I mean Grendel is a DEMON. A demon that has not been able to be stopped for 12 years and all of a sudden one man with his small army strolls up and claims they can slay the beast. I figured there would be a bit more questioning but no they just let him walk right into the kingdom for all they knew he could have just claimed a hero and pulled the old Trojan horse trick. I mean he is a hero but the watchmen don't really think twice before letting him walk into the kingdom they just take his word and let them go on his way.