In this poem, Time is personified, almost like a god, being anywhere and everywhere. Time is abstract - the progression of things. Time is also the physical evidence (concrete) of all things that exist. Time is concrete in that it is the transition through space that allows things to happen. But Time is also abstract in its personified, god-like concept. Time is, in the abstract (as pure potentiality and eventual kinetic event), the possibility of being.
The poem is divided into seven stanzas of three lines each, perhaps representing the Biblical reference to the creation of the world in seven days. In the first stanza, Time describes itself as the concrete manifestations of the moving air, the flow of water, the formation of rust, and the mileage recorded on road signs. These are all visible images that provide evidence that time is "occurring." Water can not flow if time does not flow. Rust can not form if time stops. Mileage can not be counted unless the distance is traveled.
In the second stanza, Time continues to express its presence in/of all things. Time is the "sums sole-charge teachers teach." That is to say that Time is, like the mileage, just an abstract number; a measurement of sums and calculations. With this idea of numbers, Time is an abstract number which is a measurement of an actual distance or duration of an event (such as the time taken for rust to form.)
In the third stanza, Time describes itself as being more concrete things/events: a moment in the morning, the process of a machine, and a place in a park. In the fourth stanza, Time describes how it is music/sound as well as sound that is remembered. So, Time is the actual concrete sound heard and the mind's recollection of that sound. Things happen in time and are remembered at a later time.
In the fifth stanza, Time suggests that it (Time) is abstract or exists only as the measurement of all of these concrete things.
I, Time, am all these, yet these exist
Among my mountainous fabrics like a mist,
So do they the measurable world resist.
Time is what makes these concrete things and events possible, yet Time does not exist in the same concrete way. In the last two stanzas, Time again personifies itself as a god who shapes things in the world and in memory, more than our "conscious" carriers (more than our senses and minds). In the last stanza, Time gets metaphorical (abstract) and calls itself father (God), farm (land), sea, etc. Time ends with another Biblical allusion that it/he (Time) is the Beginning and the End. Nothing exists without time.
The concrete images are the physical descriptions of objects and events. The abstract images are the ideas of Time as measurements (a number is concrete and abstract) and the idea of Time as the possibility of being.
Time provides the dimension through which things can occur (or "Be"). Therefore, Time is the transition of metal to rust; it is this concrete thing. But Time is also abstract in the sense that it is not some concrete thing we can touch. It is always already everywhere (and "everywhen"). We can see the evidence of time everywhere, but we can not see time itself.
This poem is a mediation on the slippery and paradoxical concept of time but could be interpreted as an allegory for the notion of God.