"The Seafarer" begins with an account of a harrowing journey over a winter seascape, in which the speaker endures the physical effects of winter's cold and the psychological effects of anguish and torment. Life on the sea is rough, and our guy is not a happy camper. He describes himself as wracked by sorrow and worry, unable to take pleasure in any surroundings – no matter how pleasant – because of the darkness inside himself. But somehow, by the end of the poem we realize that seafaring, and the suffering that goes with it, just might be an extended metaphor for the soul's journey to God. In that case, the suffering he endures is an essential part of the journey to eternal life.
The physical suffering the speaker describes in the poem mirrors the psychological suffering he feels. (Deep, we know.)
"The Seafarer" suggests that a feeling of inner emptiness or darkness may just be the first step on a voyage toward God and eternal life.