Why does sound matter?

Watch this without the sound from 4:55 to 7:43

Now with sound

Why is sound important? What does it add? What sounds do we hear in poetry? rhyme assonance onomatopoeia caesura alliteration meter

What are the sounds in these lines and what do they add to the tone? Boundless and bare, The lone and level sands stretch far away Cannon to right of them, Cannon to left of them, Cannon in front to them Volley’d and thunder’d Small circles glittering idly in the moon, Until they melted into one track of sparkling light. I gave commands; Then all smiles stopped together. There she stands As if alive. We are bombarded by the empty air. Strange it is a huge nothing we fear. His terror’s touchy dynamite. Sudden successive flights of bullets streak the silence. But I blink And he bursts again through the doors of the bank. The dark shoals of fishes Flashing silver as their bellies Swivelled towards the sun.

How does Tennyson convey the power of the eagle in this poem? He clasps the crag with crooked hands;  Close to the sun in lonely lands,  Ring'd with the azure world, he stands.  The wrinkled sea beneath him crawls;  He watches from his mountain walls,  And like a thunderbolt he falls.