Stanza 4 Summary

Get out the microscope, because we’re going through this poem line-by-line.

it is a power of
strong enchantment. It

And because it lands so certainly, "it is a power of strong enchantment."
Our speaker brings us out of the examples of what the mind is like to make a simple, declarative statement: the mind is powerful and fills us with delight and excitement, and maybe even a little magic.
This break from all the comparisons arrives pretty far along in the poem. Moore really makes us work through the figurative stuff before taking a breath and writing these two straightforward lines.
Don't get too comfy, though; the end of line 20 hints that she's probably going to launch right back into "it."
Plus, there is something a bit funky about these lines. Notice that she doesn't say the mind has the power of enchantment. It is the power. So rather than being just a thing here (as it was earlier in the poem), the mind is now a power.
Which makes sense in a way. After all, the word "enchantment" is a pretty powerful one, don't you think? Just reading it makes us feel like we are under some kind of spell. It reminds us of magic, and magic (to us) seems to be more about uncertainty than certainty.

is like the dove-
neck animated by
sun; it is memory's eye;

Line 21 breaks (ends) at an interesting spot. It reads that the mind is like the dove, which could mean a whole bunch of things—that the mind is peaceful, graceful, beautiful, or that it can fly. But that hyphen at the end of the line tells us that the simile ain't over yet. There's more.
Turning to the next line, we see that our speaker means dove-neck, and that this dove-neck is animated (or brought to life) by the sunlight. This is a very pretty and very specific image. So Moore is saying that the mind is a beautiful thing. And not just Russell Crowe's mind, either.
The last part of line 23 brings us another metaphor. What is memory's eye?
Well, if we connect it back to lines 13-15, we might say that the mind can see things even when it's not literally seeing.
Let's try this out. Close your eyes. Now see the Statue of Liberty. You totally can, right? Your eyes have seen about a billion pictures of the thing, so of course your mind can remember it, and call that visual image up whenever it likes.

it's conscientious inconsistency.

For the second time, our speaker tries out a straightforward statement. Sure, it's confusing, but at least it's not covered up in comparisons and metaphors.
Conscientious means diligent, or wanting to do a good job at something. Inconsistent means not getting the same result every time.
So what do these two things mean together in relation to the mind? That it's diligent about being unpredictable? It's being inconsistent, but hey, at least it's trying hard?
This short little three-word line is a bit of a mind-bender. But the mind is plenty bendy, so we'll cut Moore some slack and keep right on reading. Maybe she'll clear things up in the next stanza.