There are many reasons for developing standards (such as the Bluetooth specification). Among these are lowering the cost of product development (and hence the price of the resulting products), pooling of skills and resources in developing the standard (presumably producing a better specification than would result from proprietary solutions from individual companies), and offering consumers more choices (the existence of a standard often lowers barriers to entering marketplaces, which can result in a wider array of products; buyers need not be beholden to one or two suppliers).
Because standards can offer these benefits, there is often value for product developers in complying with standards. Buyers understand the value of standards, and may be predisposed to purchasing products that comply with them. In the domain of high technology, this seems especially true: There are a multitude of standards, many with their own qualification or certification programs; many of them have associated brands or logos that products are permitted to use after they successfully complete the qualification. Many of these logos are recognized by consumers who attach value to them.
Given this desire by product developers to comply with (and advertise compliance with) relevant standards, it would seem that something more than a simple declaration by the manufacturer that a product conforms to a given standard is needed. The role that qualification processes fill is one of defining an agreed-upon standard process (usually including testing) by which implementations can be deemed to comply with their associated specifications. Often, a qualification process includes the right to advertise this conformance (via logos or other methods) after successful completion of the qualification.
For the end user, qualification can result in some degree of assurance that a product will operate as expected (depending on the sort of certification obtained, this could relate to safety, performance, compatibility, and interoperability with other products, and so on). For example, the Bluetooth logo on a product indicates that that product has successfully completed the relevant portions of the Bluetooth qualification program, and thus can be expected to work well with other products bearing the Bluetooth logo.