Purpose and value proposition are not the same thing.  Purpose is primarily an internal message that aligns employees; value proposition is an external message that tells customers how you will meet their needs.

Customers may admire your purpose, but they buy your value proposition based on how it meets their needs.  For example, I personally admire Southwest Airlines as an organization, but I typically fly with another airline that better meets my particular business travel needs (even though I have far less admiration for their company).

Let your purpose drive you, but let your customers’ needs drive your value proposition.

“A lot of companies have chosen to downsize, and maybe that was the right thing for them.  We chose a different path.  Our belief was that if we kept putting great products in front of customers, they would continue to open their wallets.”  (Steve Jobs)