It recommends to follow the most direct and safe way to achieve something and to avoid in this way the possible problems.
Literal explanation: the path is the main route, though which all the people travel peacefully and safely; it is the widest, the best preserved and the most convenient as it is public. Outside of it we do not know what the future reserves for us. Brush concerns the field that is not cultivated and that, for this reason, it is full of undergrowth, that make it resulting uncomfortable.