Hari Om Tat Sat is a very ancient mantra from the Vedas. Hari Om is one mantra and Om Tat Sat another. I have joined the two in Hari Om Tat Sat. Hari represents the manifest universe and life. Om represents the unmanifest and absolute reality. By the word reality, I mean total existence. You may even use the word God. Reality, existence, God, Brahman, the absolute are all synonymous terms pointing to one being, but they do not really define it.
This reality has two stages. One is the absolute, the other is manifest. This gross universe, the millions of suns, moons and stars, space, that which is beyond it and beyond this little earth, as far as we can go, are all manifestations of that reality, not a creation of reality. There is a difference between the process of creation and manifestation. You take cotton and make yarn from it, and then a shirt. The cotton has become the shirt, it has not created the shirt. The cotton has transformed itself into a shirt. In the same way, there is a great invisible force. Nobody can see it and nobody has seen it, except for a few people who we call avataras.
The manifest reality, this world, is represented by the mantra Hari. Om is the unmanifest reality, the unseen, invisible, uncreated aspect of the absolute. So, Hari Om Tat Sat means That is Truth. That which I see with my eyes and that which is beyond my eyes are both the same, not different. The creator and the creation are not two. The creator has not created creation, but has manifested or transformed himself into creation.
All these truths are represented in the mantra Hari Om Tat Sat. When I say Hari Om Tat Sat, it reminds me that the seen and the unseen, are both one.