The seafarer clearly thinks that life at sea is more difficult than life on land. The first part of the poem illustrates this in detail. Life at sea is defined in terms of coldness and loneliness. Life on land is described in terms of human company and warm feelings.
But the seafarer is drawn to a life at sea. Many critics interpret this to mean that the seafarer voluntarily chooses a life at sea. In other words, it is actually something in his own mind that impels him to seek adventure at sea, in spite of his fear:
The time for journeys would come and my soul
Called me eagerly out, sent me over
The horizon, seeking foreigner's homes.
He describes more luxuries of life on land, then follows it by saying that these things admonish (warn) the type of person who chooses to go to sea. Despite these warnings and even though the life is difficult and he is away from loved ones, he is "excited" by the ocean. So, he does find something from his life and contemplation of the sea. The adventure, danger, and excitement that sailing provides are experiences that he does not think he can have on land.
The poem shifts to notions of fate and God. Part of this continues with the theme that suffering through a storm at sea is analogous to facing adversity in life. And any comforts or rewards one gets in life do not have anything to do with Heaven. Therefore, the seafarer accepts his harsh life and recognizes that if he is to consider it in the encroaching influence of Christian thinking, then he must live humbly, accept his fate and/or put his faith in God:
He who lives humbly has angels from Heaven
To carry him courage and strength and belief.