There are many predominant themes in the epic poem Beowulf. One could look at any one of them and justify their relevance in contemporary society and the universal understanding of them.
First, the theme of glory and treasure are definitely universal. Many people are out to find their place in the world: fame, fortune, and glory. Simplistically, today's society raises up the stature of those in the spotlight. Children grow up watching television and dreaming of being their favorite rock star, athlete, or movie star. The initial appeal is the fact that the people they admire have both fame and fortune.
Second, the theme of loyalty is one which Beowulf proves to be of the utmost importance. Unfortunately in today's society, many people fail to see the importance of loyalty. Instead, they are out to insure that they obtain fame and glory (see #1) at whatever cost. While loyalty seems to be important to contemporary society, it maintains a position on the back-burner of society.
Third, the theme of fate (or wyrd) is one which has been argued for centuries. The Christian faith believes in a sort of fate in their trust that God knows the path their life will take before life even began. The term fate is still used in contemporary society today given the fact that many people deem the happenings in their life as a result of fate (think, "It was fate we met.")
The universal appeal of Beowulf comes from the fact that many different cultures have similar ideologies which they have lived by for centuries.