We all incarnate with the intention to undertake a particular life mission and to learn some lessons while in the physical body. In order to assist you in your mission, you have chosen specific energies to work with. Your birth date provides the biggest clues to your 'energy blueprint' for this lifetime and it is helpful to look at whether you are making the most of such energies.
Life missions are not always serious and many people come back simply to be creative and have fun: to increase the vibrations of joy, love, beauty, compassion, grace and ease in the human collective consciousness.
My numerology teacher, David A Phillips PhD, is one of the few Pythagorean numerologists to explore numerology through the 'arrows' of energy of consecutive groups of numbers, or absence of numbers, and I have found this to be invaluable in explaining a person's driving force. I highly recommend "The Complete Book of Numerology". It is available in hard copy, but I love the Kindle for iPhone version at US$0.99.