I agree with you. “가자” sounded like "Let's go!" to me. Do you happen to have the lyrics of the song?

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가자 means literally let's go. however korean words have several meaning as u know.we are using when to chear up for someone or team and the leader who leading the followers.. u may see subtitle like 가즈아 on tv show.

As formal word yes is 예(네) We rarely use 가자(Let's go) instead of 예(네). ex) A:Do you want to go out for dinner B: 가자(instead of yes) or 좋아요(instead of yes)

hi