The three items you mention--repetition, end breaks, and enjambment--are all significantly present in "If You Saw Me Walking" by Gerald Stern. The poem is structured as a series of short stanzas, and the tone of the poem is fairly conversational. In a conversational-sounding poem, we are more likely to find non-traditional punctuation because it follows the more natural rhythms of speech instead of a more formal and patterned style.
Repetition can be a sound, a word, a phrase, a line, or a stanza in any work, but particularly a work of poetry. There is a natural rhythm to repetition, which is demonstrated in all kinds of ways other things. Consider the swinging of a pendulum, the ebb and flow of an ocean tide, the wheels turning on a train, or the churning of pistons in a machine. In fact, a swinging metronome is used to keep the rhythm of a piece of music. In this poem, then, repetition is used to create and maintain the rhythm and unity of the poem.
Note the consistent use of the words "if" and "you would" structure in the selection. The poem really is just a series of "ifs," which set up a scenario, followed by the "you woulds" which explain what the person to whom the speaker is addressing the poem would do or know about him. For example:
If you saw me swim back and forth through the algae
you would know how much I love the trees floating under me;
Too much repetition can be monotonous, and readers can easily lose interest in what they are reading. In this case, the poem is short and the repetition is effective. We know what is coming, at least in part, and that serves to draw us into the poem.
Lines that contain what you call "end breaks" are usually referred to as "end-stopped lines." Both terms simply mean that a line of poetry ends with a piece of punctuation, and there is an expectation that the logical--and even grammatical--sense of the line is completed before that piece of punctuation occurs. Stern uses end-stopped lines, but generally only in the final line of a stanza. Note the following:
If you saw me walking one more time on the island
you would know how much the end of August meant to me;
In both this example and the one above it, the second line of the stanza completes a thought and therefore ends with a piece of punctuation. Stern uses these end-stopped lines to tell us when one thought is over and another begins.
That leaves the poetic device of enjambment, which is a line of poetry in which the meaning carries over into the following line. Think of it as a kind of poetic run-on sentence. Stern uses enjambment in every stanza in this poem, as in the following short stanza:
and if you saw me burning wood
you would know I was still trying to remember the smell of maple.
Note that the first line here is not a complete thought and therefore only makes sense when read in conjunction with the line that follows.
The complexity in this poem is demonstrated by the interweaving of all three of these elements. The repeating "if" sets up a series of lines that are automatically incomplete thoughts; these "if" sentences need to be enjambed with the "you would" sentences that follow in order to makes sense; the "you would" sentences are complete sentences which need to written as end-stopped lines. Without any one of these elements, the structure and rhythm of the poem would disintegrate.