What's up with the poetry?

Poetry seems to weave its way into Grendel quite often. In chapter seven, Gardner begins to format the writing into poem lines. Grendel is known to have a sense of poetry, demonstrated when he is with Unferth '''I've never seen a live hero before. I thought they were only in poetry'" (Gardner 84). This statement implies that he has a knowledge of poetry and its common themes. It's not only the use of poems in Grendel that imply poetry, it's also Gardner's use of figurative language, specifically similes. There is an extraordinary number of similes in the novel. Some examples are:

• "The watch dogs lay like dark wet stones" (Gardner 33).
• "...their eyes rolling like a newborn colt's..." (Gardner 35).
• "...the forest looked like an old dog dying of mange" (Gardner 40).
• "I made my mind blank and fell, sank away like a stone through earth and sea..." (Gardner 56). 
• "His nose was as porous and dark as volcanic rock"(Gardner 82). 

Now after looking at all the poetry in the novel you have to remember: Beowulf was an epic poem. So, Is Gardner's choice to use poetry based purely off of Beowulf? What's the use of having all the poems in the novel? How does it change the readers view of Grendel (the character)?