Why is the focus on jobs in developing a pay structure?

When setting pay levels for positions, employees should make sure that the pay level is fair relative to what other employees in the position are being paid. Part of the pay level is determined by the pay level at other companies. If your company pays substantially less than others, it’s going to be the last choice of employment unless it offers something overwhelmingly positive to offset the low pay, such as flexible hours or a fun, congenial work atmosphere.

It needs to focus on job descriptions while developing a pay structure because it helps to arrange and to give fair pay/ salary, compensation, incentives or benefits to the employees based on the job they are perform within an organization.  Thank you.

I am sorry. Unable to understand the question. 

Job applicants will typically ask salary questions before accepting a position with your company. This information provides insight on what they can expect to earn now, as well as in the future. Different factors play a role in salary structure, and it's imperative to design a structure before interviewing and hiring staff.

There will be  a standard fixed for the job based on Employees' contribution  and their relevant job profile. While fixing it will take consideration of the industry/regional standards. The organizations with long standing in the field might have already adjusted the levels of pay  for each positions considering various parameters and practices followed. In the private sector merits of individuals will be considered for the revisions or variations.  All together the employee may  get a fair idea--how much he can expect from the new job and first decide  whether to proceed or not.

Agree with the answers given by all experts.