I am a staff at the Ministry of Religious Affairs.
Although you will occasionally find an example of staff as a countable noun, it is extremely rare.
Used as an uncountable noun, staff refers to people who work for a particular organisation:
- Staff at the Ministry of Religious Affairs receive a competitive salary.
Used as a countable noun, a staff is a kind of stick with certain features and functions:
- often very long – longer than its user is tall
- usually made of wood
- usually quite ornate, possibly hand-crafted
- used by someone with special powers, for example a wizard
- often used in specialised fighting, like kung fu
- otherwise used to assist in walking (elderly people, etc)
- He used his staff to scare away evil spirits and then used it to turn my horse into a brand new Ferrari. I noticed the staff also helped him to walk!
In the context of your writing one of these meanings, staff countable / staff uncountable, will probably be more obvious than the other. However, if you want a high score in IELTS for vocabulary, I suggest you choose the most appropriate meaning!
If you really must use a countable noun, you can do this:
- I am a member of staff at the Ministry of Religious Affairs.