It's just an expression, usually used when one is surprised! I think it's a way to get around using "God" in a casual expression like this.
Other tutors may have more ideas about this!
I agree with Writeacher. I'm sure you have expressions in Korean that express surprise.
In this context, the word "goodness" is used as an exclamation to express surprise or astonishment. It is an informal way of conveying strong emotions. This expression does not have a precise meaning, but it adds emphasis and shows the speaker's level of surprise or excitement. It is similar to saying "Oh my!" or "Oh wow!" in terms of expressing astonishment or disbelief.
