The job of a nurse is protecting everyone, first and foremost (6)
I believe the answer is:
career
'the job' is the definition.
(someone's occupation)
'nurse is protecting everyone first and foremost' is the wordplay.
'nurse' becomes 'carer' (medical worker).
'is protecting' is an insertion indicator (inserted letters are held or protected).
'first and foremost' says to take the initial letters.
The initial letter of 'everyone' is 'e'.
'carer' enclosing 'e' is 'CAREER'.
'of a' acts as a link.
(Other definitions for career that I've seen before include "Rush - occupation" , "Working lifetime" , "History of working life (6)" , "Life (in terms of work etc)" , "Vocation; rush" .)