Don't be so biased, ask why did God created humans & all other forms of life. To know the exact purpose we'll first have to understand (not believe) what is God & than the purpose of creating the entire universe & than it is time to understand human life & it's purpose. But since Yahoo won't allow me to discuss all this in detail, I'd explain (in brief) why humans are created.
if I shut my eyes and try to conceive my existence, "I," "I," "I," what is the idea before me ? The idea of a body. Am I, then, nothing but a combination of material substances ? The Vedas declare "No." I am a soul living in a body. The body will die, but I shall not die. Many ancient Hindu scriptures explain concept of life in our cosmos. In short human birth is some sort of a special opportunity to get free from the cycle of birth and death. This is the purpose of life, as humans we are given a chance to dissolve all the Karmas in order to attain liberation/Moksha/Nirvana.
God has created as we are so that we may try and fulfill our illegitimate desire of trying to be independent of God, and sooner and later understand that such an attempt is not only futile but impossible for we are part and parcel of God. The human life has the highest level of consciousness among the living beings and we have substantially more freedom/free-will than other living entities, but that brings in more responsibility alongwith for God realization is possible in these human bodies. In the Vedic texts it has been given that the other living entites (plants/animals) are not subject to the laws of karma as the human beings and those have been called "bhoga-yoni" (species we attain to experience what we deserve/desire) as opposed to the human level which is "karma-yoni". The soul in the lower species gradually comes to higher stages naturally, but in the human life we can go to anywhere from servant of God to the lowest stage as we develop our consciousness. Well, then, the human soul is eternal and immortal, perfect and infinite, and death means only a change of center from one body to another. The present is determined by our past actions, and the future by the present. The soul will go on evolving up or reverting back from birth to birth and death to death. But here is another question: is man a tiny boat in a tempest, raised one moment on the foamy crest of a billow and dashed down into a yawning chasm the next, rolling to and fro at the mercy of good and bad actions? is there no hope? is there no escape? By knowing the truth alone can one shall be saved from death over again.
Now just like a bank account, the account of our Karmas are also maintained. Most of the human beings have incarnated in a human-body due to residual Karma from previous life (this applies to animals as well). The purpose of life (incarnation) in a body/medium is to undo all the karmas accumulated over (all) the past lives. Out of the Total Karmic Account (if you will), we take a chunk of it to experience (or rather undo) in a particular lifetime. This is called Prarabdha karma. This includes good karma as well as bad karma (Sin). Some Examples of Experiencing/undoing good karma is getting a good body, good parents, good family, good education, good job, good offsprings etc. Similarly, examples of undoing bad karma could be having calamities/accidents/ enemies/losses etc. A human being incarnates in a body with Prarabdha karma. In the process, he/she does accumulates karma by acting/reacting (using freewill) to pre-destined situations (which occur due to Prarabdha). This is called Sanchita Karma (which gets added to the total karmic account) eventually. The net balance of the Prarabdha karma and the additionally accumulated Sanchita karma give rise to a grand total (at the end of one's life). This Grand Total is termed "Agami karma". Until the Agami karma reaches "0", one has to go through the cycle of births and deaths.
Taking all these for granted, how is it that I do not remember anything of my past life? This can be easily explained. I am now writing in English. It is not my mother tongue, in fact no words of my mother tongue are now present in my consciousness, but let me try to bring them up, and they rush in. That shows that consciousness is only the surface of the mental ocean, and within its depths are stored up all our experiences. Try and struggle, they would come up and you would be conscious even of your past life. As a human I’m capable of reaching this higher level of consciousness to realsie my past & to realise my future that is God :-)
Don't just blindly believe in God, understand God - this is the declaration of Hinduism & Vedas.