Here "mouth" represents what a persons says. Alternate translation: "The speech of a righteous person" (See: [[rc://en/ta/man/translate/figs-metonymy]])
This person's speech is spoken of as if it preserved living animals or people, as a water spring would do in a dry land. (See: [[rc://en/ta/man/translate/figs-metaphor]])
# the mouth of the wicked covers up violence
That is, the wicked person appears to say harmless things, but plans to violent things against other people. (See: [[rc://en/ta/man/translate/figs-metaphor]])