Don't blink, or you might miss this one altogether. It's a shorty. In "Barter," the speaker is imploring the reader to appreciate all the wonder and beauty the world has to offer. Even though the poem is only 18 lines long (broken up into 3 stanzas), Teasdale makes a pretty compelling case.
She presents "loveliness" as something life wants to "sell" us, and she catalogs some examples of the loveliness that life has in stock. From "blue waves whitened on a cliff," to the "scent of pine trees in the rain," Teasdale gives us a bunch of very sensory examples (we can see, hear, smell, what she describes) in the first two stanzas.
In the last stanza, the speaker stops listing examples of loveliness and starts in with the ol' hard-sell—telling the reader to "buy it and never count the cost." The poem ends by arguing that even a moment spent experiencing the beauty the world has to offer is worth the price of enduring all the hardships that come with life.