Base on two lines near the beginning of the poem, we can conclude that the poem's speaker is most likely an elderly man who has been a sailor for a long time and, more important, that he is an exile:
. . . how I, care-wretched, ice-cold sea/dwelt on in winter along the exile-tracks,/bereaved of both friend and kin,/behung with rime-crystals. (ll.14-17)
His exile status is repeated throughout the first half of the poem (e. g., "no sheltering kinsman brought consolation to a destitute life"--ll.25-26) to underscore that he has no family, no home, no kinsmen on land from whom he can seek shelter. We are to view him, then, as a man whose life is spent on the sea, never finding comford on land, and suffering constantly from life at its most precarious.
In a society in which a man's family and home provides a significant part of his protection throughout life, the seafarer is clearly a man with no support system:
That one does not know,/man blessed with comfort, what some endure/who widest must lay the tracks of the exile. (ll. 55-57)
At this point, however, the seafarer's tone shifts from a pure lament for his outcast state to a tone, if not of unbounded hopefulness, at least to a recognition that he has the hope of a better life:
. . . hotter to me are delights of the Lord than this dead life,/loaned on the land. I do not believe that this earth-weal still stands eternal. (ll. 64-66)
Here, he realizes that life on land, even though it might be better than life on the sea, is essentially a temporary life and that "illness or old age or else edge-hate (war)" are ways of dying with no notice for the landsman. This insight is important because it signals the seafarer's turning from the immediate personal suffering and troubles of his life as an exile on the sea to the hope of life eternal according to his Christian belief system.
The seafarer points out that "glory is humbled . . .bright face grows pale" (l.91) as men age and die; men's mighty deeds are forgotten (l.99), and all men must turn their thoughts of earthly power and happiness to thoughts of eternal life:
Foolish is he who fears not his Lord; death comes to him unexpected./Blessed is he who lives humbly: favor to him comes from heaven. (ll. 106-107)
From a dramatic monologue that begins as a very traditional Anglo-Saxon lament, with the focus on an individual man's, sufferings, The Seafarer becomes a sermon to all men on the transitory nature of life's sufferings and triumphs, and the eternal nature of the reward awaiing the man "lives humbly," whether on land or sea.