Music was a big deal for Teasdale. The way her poems sounded was probably as important to her as what they said. If you read "Barter" aloud, you'll likely hear what Shmoop is describing. The rhythmical feeling and sound of the poem are as striking as the words.
Besides the meter and rhyme we discussed in the "Form and Meter" section, Teasdale has another auditory trick up her puffy white sleeves. Sara likes repeated sounds and she uses them to link words within individual lines, giving the lines a more musical quality. Take a look at these examples:
Life has loveliness to sell (1)
Sara is showing off her mad poetry skills here with a little alliteration and consonance. She's really hitting those L sounds, but the S sounds get a lot of play too. The musicality of the line kind of mirrors the loveliness she's talking about—the symmetry of the sounds here makes the line sound lovely. Check out another:
Blue waves whitened (3)
The repeated W sound, a good example of alliteration, gives us the wa wa wa feeling of waves. This makes it easier for us to experience, to see and feel, the ocean she is describing. We need to feel it if we are going to be convinced to buy it, right? Again:
Soaring fire the sways and sings (4)
More alliteration. If those repeated S sounds don't make you want to jump up and dance, nothing will. Okay, we've gone too far. The point is Teasdale does a great deal with sound in this poem beyond simply using rhyme and meter. She's using those repeated S sounds to make the fire image more vivid, more convincing, more compelling, more likely to make us choose to buy that loveliness life is selling.
"Barter," actually, is also a good example of what, in many cases, separates poetry from song lyrics. In poetry, the words have to provide the meaning and the music. Lyrics, for the most part, rely heavily on musical accompaniment to generate feeling. When read without music, sometimes song lyrics lack the punch they have when they're heard with their musical accompaniment. Test it. Read the lyrics of your favorite song online and then listen to the lyrics with the tune. Shmoop bets the lyrics are waaaay better with the thumping base and guitars.