Browning creates an interesting symmetry between the two stanzas. The first stanza depicts the speaker's travel by water to get to his lover, while the second depicts the speaker's travel by land and eventual arrival at his lover's home. In the first, he leaves, and in the second, he arrives. In the first stanza, water is compared to fire via a metaphor that describes it as "fiery ringlets"; in the second stanza, fire is compared to water via a metaphor that describes a match igniting as a "blue spurt." Further, the rhyme scheme of each stanza follows the same pattern. In the first stanza, lines 1 and 6 rhyme, as do lines 2 and 5 and lines 3 and 4. It's similar for the second stanza, where lines 7 and 12, 8 and 11, and 9 and 10 rhyme. I've heard this pattern described as waves of rhyme, because they seem to crest in the middle of each stanza and then recede; the pattern is abccba deffed.