Here the word "voice" represents the person who is speaking. The abstract nouns "pleas" and "mercy" can be stated as "plead" and "merciful." Alternate translation: "he hears me when I plead for him to be merciful to me" (See: [[rc://en/ta/man/translate/figs-synecdoche]] and [[rc://en/ta/man/translate/figs-abstractnouns]])