Right off the bat, let's get a clear understanding of what I'm talking about. I don't mean how were you conceived or the reasoning behind your parents' desire for a family. I do mean, what significance does your life have, lived with your choices and motivations and passions. What is the grand-scale purpose of your existence on Planet Earth?
Consider the following chart.
If you really love something and the world really needs it, that constitutes a personal mission for you.
If the world needs something and you get paid for doing it or supplying it, that is a vocation.
If you are great at something and are getting paid for it, that is your profession.
If you really love something and you are great at it, that can be considered your passion.
But when all of that comes together into one thing; when your vocation, profession, passion, and mission find a single point of focus...that can be considered your purpose.
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Truth is...a purpose-driven life is so much more than a book title. To live in harmony with how God has wired you up will bring satisfaction to you and practically everyone you come in contact with. It is a union greatly to be desired.