If the core of Hinduism had to be summed up in a single word, that word would be truth, perhaps more appropriately Truth with a capital letter.
The holy syllable “Om” represents the totality of the absolute, the infinite spirit and truth.
Om is defined by the phrase Om Tat Sat meaning “Om That True.” However, each of these words represents a concept. Thus rendering Om Tat Sat in English requires a judgement call. I think a good way to say Om Tat Sat in English is “Om is the real and true infinite spirit.”
The totality of Hindu philosophy and thought is subsumed under the notion of Om Tat Sat. While the notion these words encompass may seem complex, it is really quite simple and most Hindus grasp it easily. The underlying belief of Hinduism is that only truth is real and worthy of our devotion.
The Hindu concept of God as ultimate truth is comparable with Biblical explanation given to Moses. In Exodus 3:14 God says I AM WHO I AM. SAY THIS TO THE PEOPLE OF ISRAEL. I AM HAS SENT ME TO YOU.
See Chapter 9 of On Hinduism by Irina Gajjar to explore the meaning of Truth in Hindu philosophy.
In my view, Hindu thought acknowledges the existence of multiple universes which flourish on multiple planes and/or in multiple dimensions. Hindu philosophy embraces much that goes beyond human experience and even beyond what we can fathom.
For example, ancient myths speak of many eras, many creatures and many frames of time. Time is different in the worlds of humans, of ancestors and of gods or demons. But beyond myths, ancient mathematical calculations fully anticipate the most recent and sensitive numbers regarding matters like the speed of light. Thus myths and science intersect.
Like science fiction, myths are a blend of history, prediction, fantasy and symbolism. We should not pooh pooh them as nonsense. These tales contain more grains of truth than we might think. In my view, an important truth is validation of the idea that we humans have the potential to become a multi-planetary if not multi-universal species.
See On Hinduism by Irina Gajjar
According to traditional Hindu philosophy, the mind is part of the body.
Our bodies consist of ether, air, fire, water and earth which are the five subtle elements and of the mind. The mind in turn incorporates the five senses (touching, hearing, seeing, smelling and tasting). It also embraces understanding and emotions like wanting, hating, happiness, unhappiness and courage
Thus the body and mind are allocated to the material world as distinct from the world of spirit or soul or eternity.
See Irina Gajjar’s The Gita, A New Translation of Hindu Sacred Scripture, 13: 5, 6, The Body and The Spirit