Article needed in "show (a) focus"?

Question

Recruiters prefer candidates to show a focus in their job applications.

Do we need “a” here? What would change if “a” were removed?

After all “focus” is both countable and uncountable noun.

Some dictionaries list it as uncountable, but still use indefinite article before it:

4. uncountable noun If you say that something has a focus, you mean that you can see a purpose in it. Somehow, though, their latest album has a focus that the others have lacked. Suddenly all of the seemingly isolated examples took on a meaningful focus.”
   _{Source: Collins}

The sentence comes from “Objective IELTS advanced” (Test folder 10: listening).

Recording script: “…Most recruiters well be uneasy if you’ve applied for jobs as varied as an accountant, a teacher and a sales executive: they’ll suspect that you lack the necessary focus, and they won’t expect you to be interested enough in the work, or determined enough to succeed. …”

Sentence completion task: “Recruiters prefer candidates to show a focus in their job applications.”

Answer 1

I interpret show focus and show a focus as different here: both are possible, and I can't tell which is meant.

The OED's definition 6.a for focus (n) is:

a. A point of convergence or concentration; (now usually) an object of sustained or intense interest or attention. Later also as a mass noun: sharp mental definition or prominence (cf. sense 5f).

Note that it gives different meanings for the original count noun, and the later mass (uncountable) noun.

I would interpret show a focus as "show that there is some matter which the candidate has taken as a focus and concentrated their energies on" and show focus as "show that the candidate is able to concentrate firmly on a matter".

Answer 2

The answer to your question "Do we need "a" here" is no we do not (although we might decide that we want it, we don't need it).

I think that "show focus" allows a range of interpretations - as identified by @Colin Fine.

There are a number of alternatives to using either 'a' or nothing. For example:

Show their focus - the focus of the candidate

Show relevant focus - a focus that is compatible with the role and the candidate

Show outstanding focus - focus that marks the candidate out as superior to other, less focussed, candidates.

Show the desired focus - a focus (implied on a particular set of traits or issues) on the particular traits or issues that the recruiter is interested in.

As it stands, without anything, "Show focus" is likely to be interpreted as "demonstrate the ability to focus on a matter" as @Colin Fine has identified.