Jesus compares the thoughts of a person to their good or evil treasure. The good thoughts of good people cause good actions. The evil thoughts of evil people cause evil actions. (See: [[rc://en/ta/man/translate/figs-metaphor]])
Here the good thoughts of a person are spoken of as if they are treasures stored in the heart of that person, and "his heart" is a metonym for something deep inside the person. AT: "the good things he keeps deep inside himself" or "the good things he values very intensely" (See: [[rc://en/ta/man/translate/figs-metaphor]])
Here the evil thoughts of a person are spoken of as if they are evil things stored in the heart of that person, and "his heart" is a metonym for something deep inside the person. AT: "the evil things he keeps deep inside himself" or "the evil things he values very intensely" (See: [[rc://en/ta/man/translate/figs-metaphor]])
# out of the abundance of the heart his mouth speaks
The phrase "his mouth" represents him using his mouth. AT: "what he thinks in his heart affects what he says with his mouth" or "what he values in his heart determines what he says with his mouth" (See: [[rc://en/ta/man/translate/figs-synecdoche]])