A constitution is a statement of the basic principles and laws of a nation, state, or group, such as the U.S. Constitution. Another very common meaning of constitution is the physical makeup of a person. So think of a constitution as how a body (yours, the government's) is set up. If you have a strong constitution, it means you don't get sick very often.
I think the focus of the story is on Beowulf as a hero rather than a king because it is his heroic deeds that lead to him being offered the throne. Also to be king one must possess some type of heroic qualities in order to rule a land and its people.
Beowulf tells Wiglaf that he is last one left of the thanes and it is now his job to carry on the tradition: Fate has swept away all my kinsmen, earls in their strength, to destined death. I have to go after(Norton 63) Beowulf is saying that fate has taken the lives of all of his kinsmen and he must go as well.EOWULF: The last moments In the society in which the poem Beowulf takes place, war and kingship are normal factors in daily life.