The writer speaks of his heart as if it were a container that overflows with liquid. The word "heart" represents his emotions, which are excited by the song that he sings. Alternate translation: "My emotions are excited about a good subject" (See: [[rc://en/ta/man/translate/figs-metaphor]] and [[rc://en/ta/man/translate/figs-metonymy]])
The writer speaks of his tongue as if it were a pen. He speaks words as skillfully as an experienced writer writes words. Alternate translation: "my tongue is like the pen of person who writes well" or "I speak words as skillfully as an experienced writer can write words" (See: [[rc://en/ta/man/translate/figs-metaphor]])