Yes, it is. As a general rule, English always states the subject explicitly, except in the imperative, where "you" is understand as the subject. Since "listen" has no explicit subject, we have an imperative here.

There is a punctuation joke out there that might explain it: Let's eat, children. Let's eat children. Punctuation saves lives! The first sentence is telling the children it's time for a meal. The second sentence is not good!