They cannot look out far. They cannot look in deep.
By the last stanza, we start to see the folly of the people staring at the sea a bit more. Here they are, standing around, wasting time, and all the while "they cannot look out far" and "they cannot look in deep." So what's the point, right? If they can't see far or deep into the sea, why are they staring in the first place?
If the folks along the sand are really interested in finding those elusive truths out in the sea, shouldn't they consider the limitations of their sight? After all, they don't have x-ray vision. They're only human.
Check out the anaphora with the repetition of "they cannot look." We think that amps up the matter-of-factness in the speaker's tone. Plus it hearkens back to the neither-nor of the title. Full circle, Shmoopers. Full circle.
To sum up, we think these lines are all about the fact that no matter where we look, the truth can be elusive. But it's particularly elusive if we only look at the sea. After all, all we'll ever see are the waves on the surface, and not the mysteries within.
But when was that ever a bar To any watch they keep?
The bar in line 15 isn't the place that folks go to for happy hour. A bar, in this case, is something that prevents another thing from happening. Maybe the speaker is even throwing a little pun in there with the idea of a sandbar.
Here the speaker points out that the people's limitations aren't stopping them from staring at the sea all day. Sure they can't look out far and they can't look in deep, but that's never really been an issue for humans. They're still going to look for truth, no matter what.
Heck, we do all sorts of things that seem futile, don't we? The biggest one, of course, being our search for the meaning of life and all that jazz. Or even better, what happens to us after death. A couple thousand years hasn't issued forth a concrete answer, but we keep searching anyway, no matter how little progress we make.
Notice too that the speaker isn't condemning this search for the truth, even in all its folly and futility. He seems to be suggesting instead that it's all part of human nature. We can't help but feel mesmerized by all of life's mysteries.
That final rhetorical question in line 16 helps to drive home both the speaker's point: our search ("watch") for truth may be flawed in the way we go about seeking it, but searching is part of who we are.
So the speaker's tone here sounds as if it's accepting of the people's habits since it's what we've done all along. But at the same time, the speaker sounds as if he's alerting us to the ways we might consider revising these habits. It doesn't have to be all about the sea and the "truth," in other words. We could spend sometime looking at the land beneath our feet, too.