Om is the bow, the Self is the arrow. Brahman is called its aim. It is to be hit by a man who is not thoughtless; and then, as the arrow (becomes one with the target), he will become one with Brahman.

In plain words: The sacred sound Om is the bow, your own Self is the arrow, and Brahman is the target. A person who is careful and alert can hit it. Then, just as an arrow sinks into its target, they become one with Brahman.