A job profile is the set of personality traits required for an individual to be successful in a position. It is the ideal personality for a job.
As each job within each organization is unique, the job profile should be customized to meet the specific requirements. For example, the ideal personality for an Executive Assistant will depend on a number of factors such as the personality of the executive that they are supporting, if they are supporting multiple executives, whether they will have to build relationships with other parties, the pace at which the organization operates and many more.
If you were to simply assess the personality of your candidate, you would know what traits they have, but you would not know whether the traits that they have will lead them to be successful in the position that you are hiring for. A job profile is used as a benchmark to compare your candidates to, so that you can see the level of fit for the job, as well as understand the gaps to probe deeper into in your interview process.