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.