What does this Epictetus quote mean - 'No man is free who is not master of himself'?

It means that in order to be truly free you need to be in full control of yourself and not governed by wild and woolly emotions.

ANSWER: Freedom brings great responsibility as there are always consequence to our actions. In order to avoid unwanted consequences it is better to master oneself. It is also true that those who refuse to master themselves tend to crave a master. It is better to be self governed than governed by others. If you do not master yourself, you will find yourself governed by others.