What is God in Hinduism

Concept of God

• The most ancient nations had different Deities – sun, earth, fire, water. Next come the monotheistic ideas – belief in one god.
• Hinduism since pre-historic times termed as Sanatan Dharma, believe in one “universal Brahman” i.e. Sat-Chit-Anand. Vedantic philosophy holds Brahman as creator of universe who as God created Jivatman (Souls) and physical world (Prakrati). Hence, Hindus believe in one supreme God (Mundaka Upanishad 2.2.11; Isha Upanishad, stanzas 4-8; Katha Upanishad, Brahma Samhita 5.1 etc).
• Modern science has proved the matter in the world is composed of atoms which are made of proton, neutron, electron & other sub-particles. These particles are having energy and wave functions. The laws of conservation of energy and conservation of (total) mass are equivalent and both hold true. In physics, mass–energy equivalence states that anything having mass has an equivalent amount of energy and vice versa, with these fundamental quantities directly relating to one another by Albert Einstein's famous formula : E=mc2.
• In Hinduism, Vedanta holds the view that Brahman is Cosmic consciousness (Sat-Chit-Ananda – Truth-Consciousness-Bliss) who creates universe – jivatma & physical universe, maintains and withdraws within it. Hence, Hinduism is more scientific.
• Hinduism recognised various needs and desires of human being and to fulfil them various deities & forms are invoked. Though supreme God is nirakar (formless), it manifest in many forms to fulfil the needs. As electricity takes various forms to fulfil needs of light, heat, mechanical energy etc, Nirakar God take various Sakar forms in Hinduism without losing its eternal purity &  characteristics of omnipresence, omniscience, omnipotent etc. 
• Of course, it is a better idea to have personal god though the Brahman is one supreme God, the creator of universe. Human mental frame feel more attached to sakar form of God.  
• Though all religions are essentially the same, they must have the varieties of forms produced by dissimilar circumstances among different nations.
• There is no religion that is more aware of the transcendent, timeless, formless, causeless Truth.

The concepts of Vedanta on god, relationship of Brahman, soul & prakriti (matter) and multiplicity of deities in Hinduism creation, are discussed hereunder.

Vedanta on concept of God

• Hinduism is the collective wisdom gathered by ancient rishis which are aggregated in Vedas word derived from Vid, "to know" (having two parts – Karma-kanda & Jnana-Kanda). They teach us the immortality of the soul.
• Vedanta (last part of vedas, end of Vedas) or Uttara Mimansa, reflect ideas of Upanishads. Vedantists have propounded that universe is created by one universal Brahman who is supreme God i.e. cosmic consciousness or energy.

​Relationship of Brahman, Soul & Prakiriti

• Vedanta schools varies in their views in relationship between Brahman, Ātman / Jivātman – the individual soul or self, and Prakriti – the physical universe, body and matter. Advaita School holds non-dualism / monism that Brahman is the universal reality (Sat-Chit-Ananda – Truth-Consciousness-Bliss). It creates universe, maintains and withdraws within it. Whereas, Dvaita School holds dualism that Atman (soul) and Brahman (as Vishnu) are two completely different entities. Brahman is the creator of the universe, perfect in knowledge, perfect in knowing, perfect in its power, and distinct from souls, distinct from matter.
• Monoism / Non-dualism - Prominent scholars of Advaita are Gaudapada of 5th century, Adi Shankara of 8th century CE). Later, Nathamuni, Yāmuna and Ramanuja of 1017–1137 CE), the prominent scholars propounded qualified non-dualism (Vishishtadvaita) and held existence of plurality and distinction between Atman (souls) and Brahman (ultimate reality), while re-affirming unity of all souls and that the individual soul has the potential to realize identity with the Brahman. Vallabhacharya (1479-1531 CE) propounded Shudhadvait philosophy and emphasized that prakriti (empirical world, body) is not separate from the Brahman, but just another manifestation of the latter.
• Dualism - Dvaita, founded by Madhvacharya (1199–1278 CE), held that Atman (soul) and Brahman (as Vishnu) are two completely different entities.
• Dualistic non-dualistic – Dvaitadvaita, propagated by Nimbarka (12-13th CE) held Brahman is the material cause of the universe who brings the subtle rudiments (chit - souls & achit - physical universe) into the gross form by manifesting these capacities. Dvait as all the three differ in their attributes and advait as chit & achit are dependent on Brahman.

One God many Deities

1. Hindus believe that there is one all-pervasive God which energizes the entire universe. However, they worship many deities which are confusing others. Ancient rishis in India recognized that Supreme god has created many life forms and granted varying powers and responsibilities.
2. Hindus pray to a multiplicity of Gods and Goddesses depending on their aspirations and goals. Shiva represents austerity, Lakshmi represents prosperity, Sarasvati represents knowledge, Shakti represents valour, Ganesh for removing obstacles, Hanuman for selfless service & biggest bhakta and so on. Vishnu and his avatars are at the foundation of Vaishnavism, Shiva for Shaivism, Devi for Shaktism, and some Hindu traditions such as Smarta traditions who revere multiple major deities (five) as henotheistic manifestations of Brahman. The Samhitas, which are the oldest layer of text in Vedas enumerate 33 devas as
   • 12 Adityas - sun (Vishnu, Aryaman-companion, Indra , Tvāṣṭṛ-artisan god, Varuṇa, Bhaga-wealth, Savitṛ-impeller, Vivasvat-sun, Aṃsa- celestial deities, Mitra-friend, Pūṣan-guide, Dakṣa-son of Brahma),
   • 11 Rudras -
     • Five abstractions – Ānanda "bliss", Vijnana "knowledge", Manas "thought", Prāṇa "breath" or "life", Vāc "speech";
     • Five names of Śiva – Īśāna – North-East aspect associated with all that exist i.e. peace & prosperity & represent akasha "revealing grace", Tatpuruṣa-east aspect associated with Rishi / muni & represent air "concealing grace", Aghora-South aspect associated with Rudra & represent fire  "dissolution/rejuvenation", Vāmadeva-North aspect associated with Vishnu & represent water "preserving aspect", Sadyojāta –west aspect associated with Brahma-Atman & represent earth "born at once";)
   • 8 Vasus (Dyauṣ- Father Heaven "Sky", Pṛthivī "Earth", Vāyu "Wind", Agni "Fire", Nakṣatra "Stars", Antarikṣa" Atmosphere" or "Space", Sūrya "Sun", Chandra "Moon") and
   • 2 Ashvins (twin solar deities – sunrise & sunset)
3. Hindus also believe in the reincarnation of the Supreme Being as avatars (the descent and incarnation of a deity). Two of the most well-known reincarnations Rama and Krishna.

 
 
Reference:

1. Complete works by Swami Vivekananda Volume I
2. http://veda.wikidot.com/faq
3. http://www.peakcp.com/pdf/faqh.pdf
4. https://en.wikipedia.org/wiki/Thirty-three_gods