Bob Marley Message to Mankind

Why did Bob Marley say emancipate yourself from mental slavery? Are we still in slavery in our modern era today? Mental Slavery is specifically what it means right, slavery of the mind! Still some people believe that they are free, but why shouldn't they we have free will right? I think what I want to think, I go where I want to go, and say what I want to say right? Right, then what was is message about? He then went further by saying "none but ourselves can free our minds" What? No one can free it for me, why? Well then if that's the case, how do I free my mind huh?...