( Don’t let a sin make you feel like you can’t pray. )
The question is: why is it “Make” and not “Makes” ? Even that “ a sin “ is singular.

查看翻譯

Because when you talk about letting something or someone "do something", you always use the infinitive form of the verb, regardless of the person/number of the object.

She let him read her book.
They let her ask a question.
He let me go home early.
I didn't let her finish speaking.