Here the word "mouth" refers to the whole person who speaks. Alternate translation: "I will speak wise words" (See: [[rc://en/ta/man/translate/figs-synecdoche]])
Here the word "heart" represents the mind and thoughts. The abstract nouns "meditation" and "understanding" can be translated as verbs. Alternate translation: "the thoughts upon which I meditate will help you to understand" (See: [[rc://en/ta/man/translate/figs-metonymy]] and [[rc://en/ta/man/translate/figs-abstractnouns]])