The common theme for Beowulf and Twelfth Night is that love ultimately triumphs over all things, and carpe diem (seize the day). Despite all of the conflicts, true love always wins. Also, characters must come to realize that life does not last forever and to grasp what you can and do what you must in order to live life how you want. These themes may seem to be more relevant in one or the other works, but nonetheless exists in both in several different ways.
Love ultimately triumphs over all things. This is seen as more of an obvious theme for Twelfth Night, as the entire text is centered around the main theme of love. Although some of the characters themselves were masked, they could not hide their love for each other. For example, Viola (Cesario) disguises herself as a man, and in the end, Duke Orsino discovers that he really has loved her all along. What he thought was true love with Olivia turned out to be only admiration of her beauty, but the truest deepest love that he had was for Viola.
This theme is represented by Beowulf as just another one of his heroic qualities. His love for everyone but himself was one of his more important traits for not only him, but his entire kingdom, and every future generation. He fought to help others and for those who could not, and the passion of love for others fired him up for these battles. "He's crazy. I understand him all right, make no mistake. Understand his lunatic theory of matter and mind, the chilly intellect, the hot imagination, blocks and builder, reality as stress." (pg. 151) This theme is meant to show that when the deepest kind of love is present, nothing can stop a person from defending the place and people that they love.