In plain words
that is how we breathe in. When we let it go: Ha……m. So…. Ha….m. So… Ha… m. In the oneness of these two lies the true Oṃkāra. If we recognise the inner meaning in the word So and in the word Ham, Sohaṃ: that itself is I, and that too is Tat tvam asi. Tat tvam asi is contained in three syllables. We say it is a single syllable. Om ity ekākṣaraṃ brahma. We say it is a single syllable: how does it become one syllable? So… In this, the letter S, which belongs to sārūpya, sāmīpya and sāyujya, becomes minus. When does this letter S become minus? When we forget the world and rest in the state of sleep. When we forget the good and bad of the world. In this sound So, the letter S becomes minus and it becomes simply O. In the breath going out, Ham, the letter H becomes minus. Only while we are in the waking state do the letters S and H go on merging with this Oṃkāra. When we forget this waking state and are in deep sleep, both the letters S and H vanish. When the letter S goes from the word So, what happens? It becomes O. When the letter H goes from the breath going out, Ham, it becomes M. O plus M has become Om. When the letters S and H are both joined, it has become Sohaṃ. When the letters S and H have both gone, it has become Om. That is, as long as he is in the waking state, man becomes many in this worldly life and thereby forgets the truth called Ekākṣaraṃ brahma. Only as long as this world is in our sight are there our sorrows and joys. When we enter the state of sleep, this waking world is hidden from us. When the waking world is hidden, our joys and sorrows are hidden. It is on this basis that they called sleep the state of samādhi. In that state of sleep no joy, no sorrow, no worldly world is seen by us; they do not come into our experience, they stand still.
So man must follow this kind of path to recognise Divinity. The Upaniṣads gathered what stood in great long words into small sentences, and so went on taking a form that suits the experience and the joy of ordinary people in their daily life.