These two lines share similar meanings. The second line intensifies the meaning of the first line. (See: [[rc://en/ta/man/translate/figs-parallelism]])
Elihu asks this question to emphasize that Job's sins cannot actually do anything to God. AT: "If you have sinned, you have not done any harm to God." (See: [[rc://en/ta/man/translate/figs-rquestion]])
Elihu speaks of "transgressions" as if they were objects, and of committing many transgressions as if it were piling those objects one on top of the other. He asks this question to emphasize that Job does nothing to God by his transgressions. AT: "If you committed a great many transgressions, you still do nothing to him." (See: [[rc://en/ta/man/translate/figs-metaphor]] and [[rc://en/ta/man/translate/figs-rquestion]])
The two rhetorical questions mean basically the same thing, that Job's righteousness adds nothing to God. AT: "If you are righteous, that does not enable you to give anything to him, and there is nothing that he will receive from your hand." (See: [[rc://en/ta/man/translate/figs-rquestion]] and [[rc://en/ta/man/translate/figs-parallelism]])