The essence of Creation, that which is manifest and also ...
Various cultures of the world concur that there is one Supreme Reality. But then no enterprise can be a one man show, in a company there is a CEO, and also managers, and technicians and labour and guards and so on. So how could the entire Creation be run by one alone? The vedic masters gave us the answer, ‘Ekohum Bahusyam’ (I am one, let me become many). Hence the various forms of gods and goddesses, where each is assigned a specific task or role. And one has to go through all these energies to reach the finality, or Reality. These may be seen as locks on various gates in the journey, the key to which is possessed by the Guru in the form of mantras or dhwanis. Ganpati, for example, is the guardian of the first gate, the entry.
Guru is someone who has walked the path and so has a complete understanding of what you are approaching. For example, surya dev was brought to prithvilok by Bhrigu rishi and so rishi Vishvamitra could not have reached the gayatri without invoking the shakti of his guru, rishi bhrigu. Hence, ‘bhargo devasya dheemahi…’ The Guru gave him the key to Surya. Similarly at various stages of sadhna, Guru gives the key to a sadhak to open various locks or doorways.