by the way we think of this experience. The next few stanzas present pictures from nature and reality that can be perceived in different ways. For example, "Various ducks / Shilly-shallied here and there / On the shilly-shallying water." In other words, did the ducks shilly-shally, or did the water? Later in the poem, long weeds appear to dance, and they are ignored by the shoals, and a cow wants to moo but decides not to. Again, this is about how the mind affects perception. The observer believes the cow was going to moo, but how does he know?

In the second-to-last stanza, the poet writes that his "mind observed to me / Or I to it." This contradiction asks which comes first—the mind, or the observation? The poem concludes with a final contradiction about how ordinary extraordinary things are, and how extraordinary ordinary things are. Perception plays a huge role in determining whether we think of everyday things as ordinary or extraordinary.

The style is almost like a series of haiku. A haiku is 3 lines of 5, 7, and 5 syllables respectively. But this poem does not stick to that and the lines run on even from one stanza (set of three lines) to the next, so this poem would be considered free verse. This works well because it is closely related to stream of consciousness and the poem itself is a series meditations on observations. These are observations of the external world but they are also processed as thoughts and this is one of the themes of the poem: the duality of observation. 

The first few lines, "I took my mind a walk/Or my mind took me a walk-" set up this duality. The speaker is walking around and observing ordinary things in nature and/or he is thinking about them. (It could also be argued that he is not literally walking around; he might just be thinking all this up.) The speaker is marveling at the extra-ordinariness of life and the extra-ordinariness of being able to observe it all. The "light glittering on the water" or water glittering in the light also shows the duality of observation. That is, it is extraordinary to be alive and experience things. And it is equally  extraordinary how the process of observation works.

The "water" could be analogous to your mind. The "light" is the world, observation or experience. You observe things and the "light" glitters on your mind (water); likewise, your mind glitters (thinks) in the light (world). This can get very complicated, philosophically speaking. For example, "seeing" can mean to see visually but it also can mean understanding or thinking. This isn't a mistake in the etymological history of the word "see." It reflects the way we understand external experience and internal thinking, which is that experience and thinking are quite similar. Some might say they are identical and/or they necessarily go hand in hand.

To sum up, this poem is about appreciating the phenomena of observation and the reciprocal connection between mind and the world. 

Although this was written in the 20th century and in free verse, it is quite reminiscent of Romantic poetry which was characteristically about nature and imagination.