Know thyself. For most people on the planet, this is easier said than done. The primary reason being is that we are so distracted today, not just by advertising that disempowers us, but by the basic need for survival which forces us to worker longer hours, thus giving us less time to focus and reflect on who we really are and what we are here to do. If you do find the time to reflect on this though, I think it's important to fully understand passion, purpose, vision, and their relationship with one another first, as it will make it much easier in trying to figure out your identity as a whole.
Passion is your creative emotional energy that you must authentically and continually express within the world, so as to naturally feel alive. Think of it as your natural talent that energizes you through its use, that sustains you through life, and keeps you stabilized, as well as afloat. Put another way, it is your vehicle for expressing and moving through life. It is why I symbolize it as an intricately carved ship within my own life. Once you know your passion, you'll start to feel more calm and stable inside, even when things seem chaotic around you. That's because your passion is at your heart, deep inside you.
I don't know where I am, but I'm not lost.
The Man Who Never Missed, Steve Perry
Purpose gives your life a sense of direction. Yes, knowing your passion can help stabilize you but you'll still feel frustrated because even though you can weather many storms, you'll still feel like a captain without a direction or bearing to sail by. For example, when I knew my passion, I started saying to myself "Ok, I know what I'm good at but how do I put this talent to use?" This is why I symbolize purpose as a star within my own life because it is something I can navigate by, a logical calculated bearing that makes sense to my mind.
Vision is the realization and identification of your life in context and harmony with the greater world around you. It is your passion and purpose put together, your heart and mind integrated as one. It is your life lived to its fullest. It is why I symbolize it as the destination that lies beneath the star that I sail towards with my ship. More importantly though, vision is seeing that destination in minute detail, scope, and complexity, like visualizing a magnificent city glowing along the coast of an as yet undiscovered new world.
In closing, I think Peter Senge's quote below from his book The Fifth Discipline helps to clarify purpose and vision even better using a couple of historical examples.
But vision is different from purpose. Purpose is similar to a direction, a general heading. Vision is a specific destination, a picture of a desired future. Purpose is abstract. Vision is concrete. Purpose is "advancing man's capability to explore the heavens." Vision is "a man on the moon by the end of the 1960s." Purpose is "being the best I can be", "excellence". Vision is breaking the four minute mile.