The oldest book in the library of humans is the Rigveda

The existence of the Vedas go beyond recorded history and are said to be passed down from the Gods to the great seers of Bharat. For many human generations the Vedas were passed on through word of mouth, until finally documented by the great Rishis and Swamis.

'The Vedas are written in Sanskrit, a complex language that Sir William Jones - in 1786 - demonstrated to be related to Greek, Latin, German and Celtic (giving rise to the expression 'Indo-European languages'). And if the Vedas speak of the Sarasvati River, then it would seem clear that they were written before about 2000 BC, and not later than 1500 BC, as scholars originally believed. And if - as seems likely - Sanskrit was the language of the Aryans, then it was also clear that they could not have invaded as late as 1500 BC.
There are four major collections of Vedic hymns - the Rig-Veda, the Samaveda, the Yajurveda and the Atharvaveda, of which the Rigveda is recognized as the oldest and most important.
In the 1980's, a Vedic scholar, David Frawley, observed that the hymns of the Rigveda are full of an oceanic symbolism that seems to argue that they sprang from the maritime culture - which certainly contradicted the assumption that the Aryans came from somewhere in central Europe. He also noted hymns that spoke of the 'ancestors' as coming from across the sea, having been saved from the great flood.
Studying the astronomical references in the Vedic hymns, Frawley concluded that one reference to a summer solstice in Virgo indicated a date of about 4000 BC, while a reference to a summer solstice in Libra pointed to about 6000 BC. He also concluded that the authors of the Vedas were familiar with the precession of the equinoxes. These revolutionary ideas were set out in a book called Gods, Sages and Kings (1991).

The Rigveda Samhita is the oldest significant extant Indian text. It is a collection of 1,028 Vedic Sanskrit hymns and 10,600 verses in all, organized into ten mandalas(Sanskrit: books). The hymns are dedicated to Rig Vedic deities.

Rigveda means the Veda of Adoration and mostly contains verses adoring or adulating deities. But it also dealt with other subjects, like the procedure of wedding, the folly of gambling. About two-thirds of Rigveda is about the gods Agni (Fire) and Indra (Ruler of the gods). Other Rigvedic gods include Rudra, the two Ashvins,Savitar and Surya, Varuna, the Maruts and the Ribhus. There are references to a divine creeper, the Soma, whose juice was an energizer. Some animals like horses, some rivers, and even some implements (like mortar and pestle) were deified. Rigveda contains a sense of intimate communion between Nature and the Rishis or visionaries. According to some, the concerns of Rigveda are those of simple, nomadic, pastoral Aryans. According to others, the people in the times of the Rigveda had a settled home, definite mode of life, developed social customs, political organizations, and even arts and amusements. Rigveda is the oldest, largest and most important of the Vedas, containing ten thousand verses forming 1017 poems in 20 groups.

Essentially the Rig Veda is dominated by hymns praising the God for giving them victories and wealth plundered from the local Dasas through warfare. The Aryans apparently used their advances in weaponry and skill in fighting to conquer the agricultural and tribal peoples of the fading Harappan culture. Numerous hymns refer to the use of horses and chariots with spokes which must have given their warriors a tremendous advantage. Spears, bows, arrows, and iron weapons are also mentioned. As a nomadic and pastoral culture glorifying war they established a new social structure of patriarchal families dominated by warriors and, eventually with the power of the Vedas themselves, by priests also.

Generally the hymns of the Rig Veda praise the gods and ask them for worldly benefits such as wealth, health, long life, protection, and victory over the Dasa peoples.

He, self-reliant, mighty and triumphant, brought low the dear head of the wicked Dasas. Indra the Vritra-slayer, Fort-destroyer, scattered the Dasa hosts who dwelt in darkness. For men hath he created earth and waters, and ever helped the prayer of him who worships. To him in might the Gods have ever yielded, to Indra in the tumult of battle. When in his arms they laid the bolt, he slaughtered the Dasyus and cast down their forts of iron.

Rigveda is a Veda in form of Sukti's, which mean 'beautiful statements'. A collection of very beautifully composed incantations itself is a Sukta. The Sukta is also synonymous to Richas. 'Rit' means - an incantation that contains praises and Veda means knowledge. The knowledge of the Richas or Suktas itself is the literal meaning of Rigveda.

The Rigveda Richas comprises mainly of the praises of God. Other than this it also has incantations containing thoughts which are evolved by the sages through their minute observation, contemplation and analysis. Every element of nature was an issue to contemplate upon for the sages. In this process they have randomly even spoken about the mysteries of the universe, which are not only worth reading but also for practical usage.

Rigveda is the oldest Veda. It comprises of 10 Mandals, 102 Suktas and containing 10,552 mantras. These mantras are filed with good thoughts and they have the ability to inspire us greatly. The ultimate aim of all these mantras is to purify the human mind through knowledge. Darkness is symbol of lack of knowledge or illusionary living, which makes us devoid of justness and sagacity.

The Rigveda is divided into 2 parts- (i) Mandal, Anuvak and Sukta (ii) Ashtak, Adhgaya and Sukta

According to the first division, the Rigveda consist of 10 Mandalas. There are Suktas that comprise the Mandalas. In every Sukta there are mantras or Richas. The quantity of Suktas is 1017 and the other additional Suktas account to 11. In this way, the total number is unequal. There seem to be maximum Suktas in the 1st and 10th Mandala and there are very few Suktas in the 2nd Mandala.

The following tables show the no. of Suktas and mantras in every Mandala

Mandala Sukta Number of Mantras 1 191 2006 2 43 429 3 62 617s 4 58 589 5 87 727 6 75 765 7 104 841 8 103 1716 9 114 1108 10 191 1754 10 1028 10,552

Inclusively in 10 Mandalas there are 1028 Suktas which in turn comprise of 10,552 mantras.

The Brahmanas stand second to the Vedas. The ultimate aim of these books is procedures of performing Yagya and rituals. The Brahmanas are divided into 3 parts. (i) Brahmana, (ii) Aranyaka, (iii) Upanishad

There are 2 Rigveda Brahmin texts i.e. Kausheetki and Aitereya. These 2 texts share a very intimate relation. In both these texts critical appreciation is done of the same subject and the meaning of the mantras is surprisingly contradictory. These Brahmana speak about the Soma and Rajasuya Yagya.

A big portion of the Upanishads seems to have been taken in the Aranyaka. The Aitereya and Kausheetki are the 2 Aranyakas of the Rigveda.

There are 5 texts of the Aitereya and each of these is known as Aranyaka. The 2nd and 3rd are independent Upanishads. In the 2nd half of the last 4 paragraphs are counted as Vedanta texts that is why they are referred to Aitereya Upanishads. There are 3 parts of the Kausheetki Aranyaka. The 2 parts of this Aranyaka are filled with rituals. The 3rd part is referred to as Kausheetki Upanishad.