James compares a person's tongue to a bit. A bit is a small piece of metal that is placed in a horse's mouth to control where it goes. This describes how small things can have power over something bigger. James is showing that what people say affects their lives and the lives of everyone they know. (See: [[rc://en/ta/man/translate/figs-metaphor]])
Next, James compares a person's tongue with a rudder on a ship. A "ship" is like a truck that floats on water. A "rudder" is a small piece of wood or metal at the back of the ship used to control where it goes. The word "rudder" could also be translated as "tool." James is making the same point as he was with the horse's bit. A small thing can have power over something much bigger.