“The Seafarer” is an Old English poem by an anonymous author. Composed sometime in the Anglo-Saxon period or Early Middle Ages, it reflects the poetic style of its day in that it utilizes the sound devices of alliteration and consonance, rather than rhyme.
The lines you are referring to, 59-62, exemplify the Old English style pretty well:
My soul roams with the sea, the whales’
Home, wandering to the widest corners
Of the world, returning ravenous with desire,
Flying solitary, screaming, exciting me....
Note that we hear the “s” sound 11 times in these four lines (including the “c” in “exciting”). The “s” sound is often likened to the sound of the wind, which we can imagine the Seafarer experiencing as he travels the ocean. These “s” sounds are an example of consonance because they occur not just at the beginnings of words but also in the middle (desire) and end (whales).
This wind sound is also imitated by the “wh” blend from the word “whale,” which makes an even stronger wind sound. The word “wandering,” which we see in line 60 of our modern translation, was actually “hweorfed” in the Old English version of the poem. Although it meant basically the same thing, it was pronounced like the “wh” blend we are accustomed to. In fact, it is generally thought that the Old English “hw” was pronounced with an even greater “whooshing” sound than our modern “wh,” so the resemblance to the wind would have been more striking.
Alliteration is the repetition of a consonant sound within a line of poetry. Alliteration, when used in Anglo-Saxon poetry, was used to insure the musical quality of the lyrical and elegiac poems. The poetry and epics of the Anglo-Saxon period were historically sung (by scops) given the lack of a universal written language. The alliteration helped to insure the musical quality of the poems.
The alliteration of the w, r, and s in lines 59-62 of "The Seafarer" insured the liquid sound of the lines. Since the lines in question contain specific images of water (waterways, whale path, widely, and world), the w and r illustrate the realistic and fluid movement of water. The repetition of the letters also insures the reader's fluid movement through the lines (which, again, mirrors the movement of water).