The first thing we learn about the seafarer is that he has “oft” endured hardship. This tells us that he is tenacious and determined, because he keeps going to sea in spite of this. These hardships include having his toes “benumbed” by frost, facing danger as his ship is “tossed close to cliffs” and enduring hunger.
The speaker also tells us that he is “deprived of his kinsmen,” which indicates that he is lonely and misses the human contact that he would have if he lived his life on land. He is also acutely aware of nature, and of the sound of the seabirds flying around. He thinks about moments when he pretends that bird calls were actually the sound of camaraderie with non-existent fellow sailors.
Despite all this hardship, our seafarer is a born adventurer, and one of the characteristics revealed later in the poem is a compulsion to take new journeys, despite his knowledge of the easy life that city men live. He feels the need to prove himself as a seafarer.
The fact that a large portion of this poem speaks of God, Heaven, and the soul tells us that in spite of all that he endures, the speaker has deep faith in God, and is a very spiritual person. He urges readers to perform great deeds to assure their passage to heaven.