These phrases mean the same thing and are combined for emphasis. Alternate translation: "I have sinned terribly" (See: [[rc://en/ta/man/translate/figs-parallelism]])
David uses a question and compares the people to sheep to emphasize that they have done nothing wrong. This rhetorical question can be translated as a statement. Alternate translation: "These ordinary people have done nothing wrong." (See: [[rc://en/ta/man/translate/figs-rquestion]] and [[rc://en/ta/man/translate/figs-metaphor]])