The title sets us up to start thinking about choices. When we barter, we have to make decisions about what we are going to accept in exchange for our goods or services—it's all about choice, folks. Teasdale wants to put the reader in that choosing state of mind right from the get go.
Life has loveliness to sell […] Life has loveliness to sell. (1,7)
We have a salesperson (Life) and they have a product to sell us (loveliness). Were talking shopping here and it's tough to come up with a better example of a time when choice is central. Picture yourself in the grocery store, shoe shopping, car shopping, you name it—it's all about choice, choice, choice. Fruity Pebbles or Lucky Charms? Creepers or Clogs? Ferrari or Lamborghini? Hey, this is kind of fun.
This line puts us in a shopping/choosing frame of mind right from the start and keeps the feeling going when it's repeated about midway through the poem—nice going, Sara.
Spend all you have for loveliness, Buy it and never count the cost. (13-14)
Things get a little more hard-sell in lines 13 and 14. The speaker is trying to influence the reader's choice by telling us that the cost shouldn't be a factor in our decision. Think about it. What would it be like to go shopping if money, if price, were no issue at all? Besides being a dream come true, it would make decisions a lot easier. We wouldn't have to weigh cost against necessity. No more would you have to ask yourself, "Do I really need another limited edition Jedi lightsaber?" We could just choose whatever caught our eye.
If you were shopping for a diamond ring, instead of trying to calculate how much you can afford based upon the ol' three-months' salary rule (ouch) you could choose a ring based solely on beauty—on loveliness. Sweet. This is what Teasdale is talking about—choosing to see the loveliness in the world without letting all that "non-lovely" stuff get in the way.