The angels will protect not only the reader's foot but the rest of his body as well. The words "not ... hit your foot on a stone" is an exaggerated metonym to say that not even small bad things will happen. This should probably not be taken as a promise that no bad things will ever happen again. AT: "you will not even hit your foot on a stone" or "not even the smallest bad thing will happen to you" (See: [[rc://en/ta/man/translate/figs-hyperbole]] and [[rc://en/ta/man/translate/figs-synecdoche]] and [[rc://en/ta/man/translate/figs-metonymy]])