This is the 7399th most frequent Chinese word.
莫不
"莫不" means "none or no one does not," implying "all without exception."
In this sentence, "莫不" means "no one was not" or "everyone was", emphasizing that all were affected.
面对此种景象，广大人民群众莫不为之动容。
Faced with this spectacle, the people were all moved.
Here, "莫不" is used to express that there was no exception among the residents; everyone came to assist.
当时的情况非常紧急，附近的居民莫不前来相助。
The situation at that time was very urgent, and the residents nearby all came to help.
In this usage, "莫不" conveys that it is universally true among authors that they infused their emotions into their creations.