Knowing your soul's purpose is the most important key to living a happy life. Without knowing your soul's life purpose there is no meaning to one's life. Without meaning in your life, there can be no lasting happiness. It is knowing, and then living your soul's life purpose that gives your life meaning, and through meaning, happiness.
A person who does not know what their soul's life purpose is may drift aimlessly through life-drifting from one job to another or from one lifestyle to another. Quite likely, most of the vices and escapisms that people pursue arise from an inability to know what their soul's life purpose is. Lacking such knowledge, a person may seek to escape a great void of emptiness within themselves by becoming addicted to alcohol, drugs, gambling, or neurotic relationships. Life without meaning and purpose is life without a sense of hope, inspiration, or happiness.
Every soul has a soul's life purpose for the life they are leading, whether they are consciously aware of it or not. The fortunate souls who find what their soul's purpose is, and then live it, generally have something in common. And what they have in common is God.