First, let us clear up one crucial point: "The Seafarer" wasn't written by Burton Raffel. Raffel translated this poem from the Old English (and some translations don't provide stanza breaks, so it's possible for different readers to discuss it and confusion to result).

Now, turning to the poem, the first stanza blends a wish or oath of truthfulness with a general announcement of the poem's themes: it is about a life spent at sea.

The second stanza describes the many nights spent guiding the ship.
The third describes how the poet suffered in the cold-- ice chaining him to the deck, etc.
The fourth reflects on his distance from an anonymous man on the shore, and how that person doesn't know what he goes through.
The fifth (assuming we're dividing the stanzas the same way) returns to the physical suffering he's gone through, and the sixth again discusses his isolation, rather poetically.

Taken together, they are a meditation on how completely the sea shaped the poet's life, how he has suffered as a result, and how alone the sea makes him.

Greg