I have no idea if I got the sailing/knot imagery even remotely correct. Just taking a guess to get started with this poem.
Terms (from poetryfoundation.org)
On land any length of rope that’s hitched
to something beyond itself and takes
the strain is called the standing part.
Tossed over a beam or limb, with a slipknot
tied in the farther end, the standing part
could be said to end in a noose. At sea,
put to use, rope changes its name to line.
The part spliced into an eye or, say,
made fast to a shackle, the part that does
the work, that works, remains the standing part.
Any loop or slack curve in the running part
of the line, the part that’s not working, becomes
a bight; and the part of the running part
that’s let go, or finally eased off
until there’s no reserve left, is known
as the bitter end. As it is in other events,
ashore or at sea, that come to the end of the line.
“Terms,” “hitched,” “part” – this looks initially to be some kind of comment on marriage gone bad, especially if one keeps in mind the last line: As it is in other events, ashore or at sea, that come to the end of the line. We don’t need to read too deeply into the first three lines to realize, with that assumption, one partner is taking all the “strain” of the relationship. But the next three lines prevent us from ascribing all virtue to the “standing part,” given that the “standing part” seems to make “till death do us part” a bit too literal.
The poem changes the scene from land to sea. Perhaps a generic conflict is being adumbrated. One partner wants security: things and people are held secure, in one place. The other wants freedom. The change of scene is accompanied by a change of terms. A “rope” is now a “line.” It seems, ever so briefly, to be something entirely different from how it was conceived on land. Instead of stemming from a “limb,” it is associated with an “eye.” It isn’t here to hang anyone – oh wait, it’s being “made fast to a shackle.” And there is still a part that “works,” and it is called the “standing part.”
The “bight” and the “bitter end” work together to form a solid knot. The “bight” – the slack in the line – is intentional in a bowline, and resembles an eye at first and when the knot is complete. It is “not working” only in the sense it is seeing ahead. The “bight” could be said to be a “standing part,” and if we are talking about a “bowline” knot, it seems to be a knot with general application. The “bitter end” seems unsecured (“let go”), but in all sailing knots (again, from what I can tell from reading about knots for 5 minutes), it is the part one is actually working with. It is only “let go” or “eased off” because the knot has already been formed.
So yeah, at this point, I’m pretty confused. I think the change from “land” to “sea” is the key to the poem. On “land,” things are very simple: you’re tied down, and that’s that. But if one sees life as complicated in any way – as not fundamentally static – then it is vital to have something that holds back, who can see what it is the couple should tie themselves to. Of course, once that is said, a trap has been laid. Doesn’t marriage depend on a vision of the eternal, and only the eternal? The change from “land” to “sea” seems to involve partners stepping outside of the roles they had on “land.” One partner isn’t a “standing part” that’s right about everything and never changes, and another partner isn’t always looking elsewhere, seemingly distracted. Each partner does whatever it takes to make the knot secure. Of course, the irony is that people do sort themselves into fixed roles, and marriages may suffer an incredible strain from their doing so.