Certain uncountable nouns are used with a/an when we are limiting their meaning in some way. Most of these nouns refer to human emotions or mental activity. Examples are: knowledge, distrust, understanding, hatred, education

We are looking for a translator with a first-class knowledge of Spanish. (NOT We are looking for a translator with first-class knowledge of Spanish.)

Even as a child she showed a surprising understanding of adult behavior.

I want my kids to have a good education. (NOT I want my kids to have good education.)

Do you think that a good education is more important than a good upbringing?

Note that these nouns cannot be used in the plural. We can’t, for example, say educations, understandings or knowledges.

Most uncountable nouns cannot be used with a/an at all.

She speaks excellent French. (NOT She speaks an excellent French.)

Everybody should be able to enjoy good health. (NOT Everybody should be able to enjoy a good health.)

It is interesting work. (NOT It is an interesting work.) (But you can say: It is an interesting job. OR It is an interesting piece of work.)

He gave me some advice. (NOT He gave me an advice.) (But you can say: He gave me a piece of advice.)