I don't think Gurus taught about any God. They taught about one supreme primordial reality which is substratum of everything. It is my perception that modern Sikh scholars have taken the Christists picture of HInduism as Hinduism and have tried to diffrentiate Sikhism from Hinduism. A spiritual system ( i don't consider Abrahmic cults to be spiritual systems they are theological system) is known by its philosphy not by its rituals. Rituals are mere means not the goal. Goal is the realization of the truth as claimed by the Philosphy. In this light i don't see how the "Akal Purush" of the Granth Shahib is different from the "Brahmn" of the Vedas. The insights of Nanak are as typically Hindu as you can get.
The Self, the objectless self-contained consciousness, is nirguna, beyond the qualities that make for difference between human beings. As a contemporary spiritual teacher said: “What is Self-realization? By what does a ‘realized’ person distinguish himself? Very simple, the special thing about him is this: one who is ‘realized’, realizes that he is the same as everybody else.” The Self has no separate identity, neither individual nor communal.
When we get to this conceptual level, we can see that communal identity in Hindu-Sikh tradition is a superficial reality, relatively acceptable and inevitable in the temporal world, but unreal from the angle of the timeless and colourless Self. By contrast, it has an absolute value in Islam, which decides on eternal heaven and eternal hell on the basis of communal identity: as per the Quran, all “unbelievers” (Sikhs as much as Hindus) carry a one-way ticket to hell. At the fundamental level, for all its adoption of external elements following Islamic models, Sikhism is not a middling position between Hinduism and Islam. Sikhism has never repudiated the doctrine of the Self, which is entirely non-Islamic and entirely Hindu.
Everything that is said to be unique to Sikhi is not so unique in reality but is a reiteration of ancient Indian philosophy which later came to be known as Hinduism. The differences between Hinduism and Sikhism are not in philosophy but in appearance, and some in the practice of casteism and ritualism. Aim of both Sikhism and Hinduism is not to secure heaven or even a better life in the next birth, but to secure happiness here and now and attainment of the supreme One, Parabrahma, infinite Bliss hereafter.
There are various names of Brahman, the Supreme One used in Hindu scriptures, by which Guru Nanak has also addressed Him. Some of them are, Onkaara, Parabrahma, Brahman, Satnaam, Aatman, Truth, Gobinda, Daamodara, Rama, Nirankaara(Formless), Naam, Shiva, etc. Upanishadic seers never recommended rituals for realization and did not condemn the worship of various deities, but informed the believers the limitations thereof and then led them to the infinite Bliss. Similarly, with the same synthesizing attitude, Guru Nanak used the same names liberally to convey the utter unity of Gods in Non–dual (Advaita) and Dual (Dvaita) systems of thoughts.
Guru Nanak himself used the authority of Vedas to explain his philosophy of devotion. He asks the disciples to meet and listen to the Vedas, ‘Smrities’, the six scriptures, and ‘Puraanas’, and meditate on Brahman to attain Him. He goes to the extent of stating, “Those who read and recite Vedas etc. without a The Guru would have doubts and therefore would not understand the Reality, they would earn sorrow and misery.“ One, who understands the fundamentals of Vedas etc., realizes the Supreme here and now. And if such an enlightened person preaches everyone regardless of their castes etc, then The Guru Nanak would salute him”. He further says that wisdom for persons of all castes lies in performing their duties, but he who knows that the path of devotional chanting is the same for all, he serves Him, he indeed becomes the Supreme One. The concept of god in Sikhi is not so unique afterall.
It has been shown that faiths and important philosophical concepts used by Guru Nanak are the same as used in various Hindu scriptures for ‘Advaitic’ and devotional school. It may be borne in mind that Hinduism has three other schools for the same goal.
Just as a single force in space can be mathematically conceived as having various spatial components, the Supreme Being or god, the personal form of the Ultimate Reality, is conceived by Hindus as having various aspects. A Hindu deity (god or goddess(note the small 'g'); represents a particular aspect of the Supreme Being. For example, Saraswati represents the learning and knowledge aspect of the Supreme Being. Thus, if a Hindu wants to pray for acquiring knowledge and understanding, he prays to Saraswati. Just as sunlight cannot have a separate and independent existence from the sun itself, a Hindu deity does not have a separate and independent existence from the Supreme Being. Thus, Hindu worship of deities is monotheistic polytheism and not simple polytheism.
Hindus declare that there is only one Supreme Being and He is the god of all religions.
Hindus view cosmic activity of the Supreme Being as comprised of three tasks: creation, preservation, and dissolution and recreation. Hindus associate these three cosmic tasks with the three deities, Brahma, Vishnu and Shiva. Brahma brings forth the creation and represents the creative principle of the Supreme Being. Vishnu maintains the universe and represents the eternal principle of preservation. Shiva represents the principle of dissolution and recreation. These three deities together form the Hindu Trinity.
One must clearly understand that Brahma, Vishnu and Shiva are not three independent deities(the Human form attributed to them is mere artistic expression). They represent the same power (the Supreme Being), but in three different aspects. Just as a man may be called a doctor, father or husband based upon the tasks he performs, the Supreme Being is called Brahma, Vishnu or Shiva when conceived as performing the three different cosmic tasks of creation, preser-vation, and dissolution/recreation.
Hindu religion is often labeled as a religion of 330 million gods. This misunderstanding arises when people fail to grasp the symbolism of the Hindu pantheon. According to the Hindu scriptures, living beings are not apart from god, since He lives in each and every one of them in the form of atman. Thus each living being is a unique manifestation of god. In ancient times some poet probably got the idea that there were 330 million living beings. This gave rise to the idea of 330 million deities or gods. Actually, this vast number of gods could not have been possibly worshipped, since 330 million names could not have been designed for them. The number 330 million was simply used to give a symbolic expression to the fundamental Hindu doctrine that God lives in the hearts of all living beings.
Indic faith system is perhaps the only tradition that is so diverse in its theoretical premises and practical expressions that it is like a compilation of religions. Hinduism can never be neatly slotted into any particular belief system — monism, theism, monotheism, polytheism, pantheism, panentheism — for all these systems are reflected in its many facets.
Hinduism lacks any unified system of beliefs and ideas. It is a phenomenon and represents a broad spectrum of beliefs and practices which on one hand are akin to paganism, pantheism and the like, and on the other very profound, abstract, metaphysical speculations.
Thanks