The Vedas. The Rig Veda.

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The Rig Veda is the oldest of the Vedas. All the other Vedas are based upon it and consist to a large degree of various hymns from it. It consists of a thousand               such hymns, each hymn averaging around ten verses.

The Rig Veda is the book of Mantra. It contains the oldest form of all the Sanskrit mantras. It is built around a science of sound which comprehends the meaning and power of each letter. Most aspects of Vedic science like the practice of yoga, meditation, mantra and Ayurveda can be found in the Rig Veda and we still                  use many terms that come from it.

While originally several different versions of the Rig Veda were said to exist, only one remains. Its form has been structured in several different ways to guarantee its authenticity and proper preservation through time.

The practice of chanting Hymns dates back at least 3,000 years and is probably the world's oldest continuous vocal tradition. The earliest collection, or Samhita, of Vedic texts is the Rig Veda, containing about 1,000 hymns. These are chanted in syllabic style--a type of heightened speech with one syllable to a tone. Three levels of pitch are employed: a basic reciting tone is embellished by neighboring tones above and below, which are used to emphasize grammatical accents in the texts. These Rig-Veda hymns are the basis for a later collection, the Sam-Veda.

Although there are other Vedas written, the most important is the Rig Veda, which contains over 1,000 hymns directed to the Gods.  The content of these hymns includes praises, blessings, sacrifices, and curses.  These hymns are the major way in which we praised  Gods.  The subject of the hymns is the personification of the powers of nature.  The hymns are written in poetic form:
"This light hath come, of all the lights the fairest,
The brilliant brightness hath been born, far-shining,
Urged on to prompt the sun-god's shining power.
Night and Morning clash not, nor yet do linger." 
Every hymn has very poetic language.  This can be chanted, creating a worshipful mood in a person. When you chant these words, you are transported into another state of mind.  At the end of the Rig Veda, 
The scholars added a summary of the philosophy of the Veda. The Upanishads became the basis of Hinduism.  They serve as a summary of all of the knowledge of the Veda as well as a commentary on them.
The religion that sprang forth from the Vedas helped shape the society.  For example, the Rig Veda and Vedic literature were used in the development of the caste system.  The Rig Veda describes how the God Purusha sacrificed himself. Each of the pieces of his body developed into a different portion of society. His mouth became the priests; his arms became the Kshatriyas or warriors; his thighs became the Vaisya or merchants, farmers, herders and artisans; and the feet became the Sudra or slaves and servants. Thus, while each part of society had its own role, it was still and a single body.