When we are introduced to Mary Oliver's poem Heron Rises from the Dark, Summer Pond, we immediately get a sense of the size, grace and elegance of this "long-necked, long-bodied," bird. The shape of the poem itself - short verses, short lines - adds to the visual picture created.
There is repetition of a few key words such as "long" in the body and the neck and later the long legs so that the reader, if he or she is not familiar with the heron can be sure to imagine it. In flight, the heron can be recognized as its legs trail behind and this poem contributes to that image. Long is also used as the "summers are long,"such as life may be long but ultimately, the path is the same and there is hope and almost certainty - "a common thing"- that death is so much more than a "hole in the ground."
"Heavy" is also repeated, used right at the beginning and again right at the end so that, although herons themselves are not heavy, we do not forget the effort involved in flight - as easy as it looks! The heron's take off is slow and seems to have great purpose just as life takes its path and has a purpose as "a new life" awaits.
Mary Oliver wants readers to understand that the existence of life after death is almost proven by the action of the heron. Therefore the subtle use of repetition gently persuades the reader.