Many times poets uses line breaks to help the reader better understand the poem. Most or all of these poems are written in free verse, meaning the poet has the option to place the break anywhere in the poem. The place of the break is very important and there is usually a reason to why the poet placed the break in that certain spot.
In "A Sort of a Song," Williams using the famous text "No ideas but n things" as a break in the poem. This particular line is used to so that the reader can understand the meaning of the poem. Not only does this text move away from the common rhythm of the poem, but it also presents the meaning in a different way. Williams placed this break as the second to the last line of the poem to add more meaning to the break. The poem starts by comparing language to snake. He mentions "to strike, quiet to wait,..." By saying this, he tries to explain the power of language and how useful it can be. Then he goes on and gives this break in the second paragraph, right before he mentions:
"Invent!
Saxifrage is my flower that splits
the rock."
The break tells the meaning and then Williams, commands the reader to do something about it. He says uses the language in real life and break away from the personal isolation.
The place of the break in the poem adds a special meaning and creates a different setting. Some poets uses this break in the beginning of the poem, some as the last sentence, some in the middle and others right before a command like Williams. Williams places the break in a spot in which the intro has already been given, the meaning (break), and tells the reader to act on it (since they know what it means now).