The most ancient scriptures in the world are supposed to be 'Vedas'. The Vedas have been divided into four parts: Sama Veda, Yajur Veda, Ŕg Veda and Atharva Veda.

 This is the story of the true origin of Vedas from Srimad Bhagavatam:

     Once upon a time  The great sage [Vyasadeva], as the sun rose, took his morning ablution in the waters of the Sarasvati and sat alone to concentrate. Vyasadeva saw anomalies in the duties of the millennium. This happens on the earth in different ages, due to unseen forces in the course of time.

     The great sage, who was fully equipped in knowledge, could see, through his transcendental vision, the deterioration of everything material, due to the influence of the age. He could also see that the faithless people in general would be reduced in duration of life and would be impatient due to lack of goodness. Thus he contemplated for the welfare of men in all statuses and orders of life. He saw that the sacrifices mentioned in the Vedas were means by which the people's occupations could be purified. And to simplify the process he divided the one Veda into four, in order to expand them among men.

     The four divisions of the original sources of knowledge [the Vedas] were made separately. But the historical facts and authentic stories mentioned in the Puranas are called the fifth Veda. After the Vedas were divided into four divisions, Paila Sage became the professor of the Rg Veda, Jaimini the professor of the Sama Veda, and Vaisampayana alone became glorified by the Yajur Veda. The Sumantu Muni Angira, who was very devotedly engaged, was entrusted with the Atharva Veda. And my father, Romaharsana, was entrusted with the Puranas and historical records.

     All these learned scholars, in their turn, rendered their entrusted Vedas unto their many disciples, grand-disciples and great grand-disciples, and thus the respective branches of the followers of the Vedas came into being. Thus the great sage Vyasadeva, who is very kind to the ignorant masses, edited the Vedas so they might be assimilated by less intellectual men. Out of compassion, the great sage thought it wise that this would enable men to achieve the ultimate goal of life. Thus he compiled the great historical narration called the Mahabharata for women, laborers and friends of the twice-born.

     Knowledge part of the Vedas is called the Upanishads and it is normally accepted that knowledge part is enough for a spiritual aspirant to understand the supreme principle of Vedas. The Upanishads are many and were added to the principal ones later. Even the principal Upanishads except a handful maybe suspected to be added decades after the vedic age. The principal Upanishads are only highlighted for a normal spiritual discourse, as the content is repeated in other later added Upanishads. There are at present about 108 Upanishads and in these, only about a handful Upanishads are supposed to be classified in the principal category.

     The Concept of Gods are dealt in a very casual way in upanishads and when we go deep into the vedas for original verses and later added ones for the benefit of a particular caste called "The Brahmins" of whom the later benerations proved to be less interested in practising the principles than exercising the verses for material gains from kings and common people. This was understandable on the grounds of vedas itself as the upanishads describe the material desire and urge to be far more powerful in the later generations- as the gunas or qualities mix in the space time continuum and the mixing would be having a direct impact on the ideas of the individuals born in the degraded bythos or maya leading to inferior genetic make up and thus more materialistically oriented offsprings for future generations.

      It may be rather pretty unproductive for a pure spiritual aspirant to wad through the thousands of shlokas or verses of all the vedas, which consists of mostly hymns and prayers to the lesser gods and goddesses and the later added verses makes it pretty more difficult to comprhend the real meaning and purpose of some of the verses- in context to the real purpose of a search for the true meaning of life. Reading the upanishads is the alternative to a spiritual aspirant who is very eager to delve into the mysteries of hyperspace and still do it in a very short time. Each Upanishad verse has hidden meanings which reflects the vastsness and complexity of the supreme consciousness and the upanishads never ever ask you to blindly believe in a supreme power and instead demands that the pursuit for true wisdom be kept vigilant without biases until the inquiring soul is pretty sure of the existence or non existence of a single energy source for the whole universe. The Vivekachudamani of Sri Shankaracharya is a much enlightening scripture in this matter; as it explicitly explores into the human nature and the mystery of mind as a flitting type of mirrored consciousness and he establishes by reasoning the existence of self beyond death and senses.

      As we understand and contemplate deep and long into the enigmatic verses of the principal upanishads stripped of our racial discriminations and id, libido and super ego's( as the freud may describe the gunas in rather naive terms!);  being the beings we are- to be slaughtered by some unseen heart blocks by cholesterol deposits or motor accidents or poisoned or getting shot at or stabbed or just getting old and dying - in some unseen future point in the arrow of time (but surely within 100 years!- time alloted for us to die!!!); we would rather be sitting and thinking about the meaning of and the purpose of life not only ours but of each and every moving and wiggling things we see around us everyday in our rather busy life, in which we are so engrossed in making it comfortable for us to live here that when we make it all; it is time for us to die and leave all those!!! Rather cute phenomenon, don't you think? In the process of getting to the top and struggling to stay there; our egos never rest to think about the rotten and dissipated state of body tissues that we so eagerly try to preserve in a pristine form at all costs, till we die...

     As we normally judge an intelligent person by whether he has succeded in making him comfortable in his lifetime by his wealth, power and attitude; I would rather suggest any of the more intelligent persons with a cut above the rest to understand and contemplate on the verses of the upanishads to be classified as an intelligent soul to be successful in not only in this life, but also in the life beyond death. Most of all, this knowledge is free to take and to be used as; indeed, " We are children of the most high"  like said in the Bible (and Qur'an) and not of the lesser gods or watchers of whom I would be briefly mentioning elsewhere. I would personally like to recommend a really openminded person to read through the upanishads by using links and then read carefully the yoga vasishta section- for a general understanding of the basic principles of Life and Death... As I would rather like to Call it...

The Upanishads - Excerpts From The International Gita Society