Dear Gurudev, what is the significance of focusing on our nose?
Just above the nose is the agyachakra, the commanding center of consciousness. The center between the eyebrows is called the commanding center which brings wakefulness in your mind. So bringing your attention to the nostrils is a prelude, it helps the frontal cortex in your brain to balance and be active in a restful state.
When you have sensual or sensory experiences, the back of your head is mostly active. Also when you are not very alert, not very conscious then the back of your head is active.
When your frontal cortex is active then attention and focus are present and the quality of awareness shifts. This is an ancient technique.
We have 3 dimensions, body, breath, and mind. Each of them have their own rhythm but they are all linked. This attention can synchronize all three dimensions.