In the first stanza, the stressed syllables are as follows:
the WRINkled SEA beNEATH his CRAWLS;
he WATCHes from his MOUNtain WALKS;
and LIKE a THUNderBOLT he FALLS;
The stressed syllables are emphasized to create a rhythmic pattern in the stanza, known as meter. In this case, the meter is primarily iambic tetrameter, which consists of four iambs (an unstressed syllable followed by a stressed syllable) per line.