The breadth of Hindu religion accommodates a large variety of religious concepts. Sarvepalli Radhakrishnan called it'Hindu hospitality'. As a result we see varied forms of practice of Hinduism. From the surface it may even appear like different religions with no common thread or goal. Shankaracharya (788-820 C.E.) was responsible for the 'synthesis' of Hindu religion. But for the effort of Shankara, the chaotic and disorganized practices of many factions of Hinduism probably would have resulted in many splintered groups of religions. Shankara brilliantly unified the different practices into one religion that we call Hinduism today. Though the diversity continued, they were now under the large, hospitable umbrella of Hinduism or Sanatana Dharma.
The concept of God in Upanishads is the 'Brahman' or the Universal Soul (synonymous with The Absolute, Supreme Being or World Spirit ' param-atman). Every human being has an atman (individual soul - jiva-atman) that resembles the Universal Soul that is temporarily separated from It. It is compared to a fire that is the Supreme Being, from flames of which come the sparks, which are the human souls. However, the human soul has an undiminished desire to join its creator. The newer religions like Christianity and Islam also profess that God created man in His own image. The goal of every human, in all religions, is to 'seek and find God'.
Brahman of the Upanishads is the impersonal, transcendent power that is responsible for all creation and the cosmos. This World Soul can only be described as what it is not, only in negative terms. It is nirguna (without qualities), nirakara (without form),nirvishesha (without particularity) and nirupadhika (without limitations). In Brhadaranyaka Upanishad, when Yajnavalkya was questioned by his students to describe God, he could only say, 'It is not this and it is not that' (neti, neti, neti). This unlimited, amorphous, colorless, characterless and formless Universal Spirit is omnipresent and omnipotent and like cosmic energy, it is pervasive, unseen and indescribable. There is, however, a danger of describing the Supreme Being in negative terms. This renders it totally impersonal and dispels a positive image of God. Buddha circumvented this problem by calling the eternal spirit nothing but righteousness or dharma, the codes of ethical living that all humans should follow. Buddha said that the cause for all suffering was sorrow (dukkha) and it can only be countered by renouncing 'thirst' (tanha, desire), by living a life of moral and ethical standard (refer to Four Noble Truths and the Eightfold Path). To attain nirvana, Buddha suggested taking a non-extreme course called the Middle Path. It is the essence of Buddha's dharma teachings. This path is between extreme self-denial (as in Jainism) and indiscriminate self-indulgence (as in the materialistic Charvakas). Though atheistic at its inception, Buddhism ultimately used Buddha himself as its icon and God. Eventually, even Hindus accepted Buddha as one of Vishnu avatars.
Ordinary people (Hindus) needed a God they could conceptualize, for worship. To go about their daily lives with devotion, the common folks needed a symbol, a personal God. Upanishads that described Nirguna Brahman as the Universal Soul also offered a Saguna Brahman, who is the antithesis of Nirguna Brahman. SagunaBrahman, who is the manifested form of the World Soul, is full of attributes and character. It is a perfect being, perfect consciousness and perfect freedom (sat-chit-ananda). Hindus have perceived Saguna Brahman as different godheads to be worshipped. As the religion evolved, came into popularity - Shiva, Vishnu and Shakti, all different manifestations of the Supreme Being. Later many more god-figures appeared as avatars and incarnates, all emanating from the above three. A trinity of Gods-Brahma the creator, Vishnu the preserver and Shiva the destroyer-also became popular. Shakti (same as Durga and Kali) became the mother goddess. Imbued with deep devotion, a Hindu could now worship any icon, sometimes in noisy rituals and sometimes in quiet contemplative meditation, which would have been difficult with only an abstract, negative 'non-entity' like Nirguna Brahman. But the central belief of Hinduism remained unshaken that all these forms of godheads sprung from one Universal Soul. This makes Hinduism unique in the sense that it is a monotheistic religion with a pantheon of manifested forms of God. The common misconception that Hindu religion is polytheistic is simply untrue.
Shankara is credited with bringing unity to Hindu religion when it was dangerously close to schism, especially between Shaiva and Vaishnava cults. He introduced thePanchayatna form of worship, which recognized five different godheads as part of Hindu religion. This effort effectively brought organization to the religion and also gave the individual devotee freedom of worship. Shankara called the daily struggles of man an illusion (maya), a puppetry (lila) played by God's hands. This is a significant phase in the life of a human soul, but only in a marginal way. The human soul functions in another plane, a second level of truth, vying to rejoin with the Universal Soul. The Absolute, however, is responsible for many transformations of the empirical world though the events of the daily world are deemed as illusions. This transformation depends on the three gunas that govern the events of the world. They are sattva (goodness, virtue), rajas (power, passion) and tamas (dullness, inertia). All earthly events, like the laws of nature, are guided by one of the three gunas or a combination thereof. There should be a balance between them for harmonious workings of the world. Disequilibria will lead to chaos, war, suffering, corruption and destruction. The concept of gunas is well documented in Sri Krishna's rendition of the sermon (Bhagavad-Gita) to Arjuna in the battlefield of Kurukshetra. (Also refer to Kapila's Sankhya philosophy).
Hindus also believe in the laws of karma. All actions, intended or unintended, result in karma. It is the account of a person's action. Karma is independent of God and religion. Apostasy from religion does neither absolve nor vitiate one's karma. God does not enjoin man to behave in a certain way. The basic guidelines of ethics and truth are described in the Hindu Dharma document (Dharmashastra of Manu) but the actions of a person are left to his or her discretion. However, there are consequences for all karma, good or bad, and these are permanently etched in the 'memory' of the soul. The soul carries this memory of karma, like a shroud around it, from birth to birth (punarjanma). When enough good karma is accumulated, the soul is liberated (moksha) from the cycle of births (samsara), to be eternally linked to the Absolute or the Universal World Soul. The manner of this linkage between jiva-atman andparama-atman, differs in the three major philosophies of Hinduism ' Advaita, Vishishtadvaita and Dvaita.
The concept of retributive justice that follows karma is a deterrent to immoral life and a strong incentive for a person to live an ethical and decent life. This surely helps in social harmony and brings about societal stability. The concepts of karma, gunas,parama-atman and jiva-atman in Sanatana Dharma are unique and extraordinary.