Indefinite Article Before Uncountable Nouns

This is an interesting question. Here are the relevant examples:
When I was young, people had a healthy respect for the law.
They had instilled in him a respect for his traditional culture.

We often teach that uncountable nouns have no plural and, as their name suggests, refer to things that can’t be counted; so how can they be preceded by the indefinite article, whose use implies something that can be counted?

The answer is that while uncountable nouns don’t have plurals (usually, although there are exceptions to that rule too) they can in certain circumstances be preceded by an indefinite article. These circumstances are when you are qualifying or limiting the noun’s meaning in some way. So normally we use abstract nouns like love, joy and consideration without an indefinite article:
Children need a lot of love and affection.
Penny could have shouted with joy.
She treats all her patients with consideration and respect.

But if we are talking about a certain kind of love or happiness, for example, or respect for a particular thing, then we use an indefinite article:
Theirs is a love that will be put to the test.
You’re going to spend your life chasing a happiness that always eludes you.
I want my daughter to develop a healthy respect for danger but not to live in fear.

The meaning of respect that is being described is of this type, hence the use of the indefinite article.

As for uncountable nouns that are used in the plural: we use the plural when we are talking about different types of a substance that is normally uncountable:
Customers can choose from dozens of different teas.
Believe it or not, the body does not distinguish between natural sugars and processed sugars.

Nouns that behave in this particular way are often categorized as mass nouns.

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