Possible meanings for what "all flesh" represents are 1) all human beings or 2) all physical beings, including humans and animal. (See: [[rc://en/ta/man/jit/figs-synecdoche]])
How a person behaves is spoken of as if it were a way or road. Alternate translation: "had stopped living the way God wanted" or "had behaved in an evil way" (See: [[rc://en/ta/man/jit/figs-metaphor]])