After teaching at the mandir last week a student came up and asked, "Why do we gaze at the space in between the eyebrows when we chant Aum and during certain asana?" So, I defer to the great Hatha Yoga Pradipika, Chapter 4 verses 36-38.
With internalized (one-pointed) awareness and external gaze unblinking, that verily is Shambhavi mudra, preserved in the Vedas.(36)
If the yogi remains with the chitta and prana absorbed in the internal gaze motionless, though looking, he is not seeing, it is indeed shambhavi mudra. When it is given by the guru's blessing, the state of shoonyashoonya arises. That is the real state of Shiva (consciousness).(37)
Shambhavi and kechari states, though there is a difference in the place of concentration or influence, both bring about ecstasy, absorption in void, in the experience of chit shukha or the pleasure of consciousness.(38)
Regular practice of Shambhavi is reputed to strengthen and stop the degeneration of the pineal gland, and because of this it is recommended for children eight onward to help with emotional development (under competent guidance of course). When practiced, the calming effect is evident as it help to relieve mental strain and emotional stress. It develops concentration and when taught by your Guruji, as said in the quote, can lead to the state of Shiva.
In Asana Pranayama Mudra Bandha it says:
Shambhavi is the wife or consort of Shambhu and both are aspects of Shakti and Lord Shiva. According to the tradition, Shambhu taught Shambhavi the practice of shambhavi mudra as a means of attaining higher awareness. It is said that practicing this mudra will stir Shambhu and make him appear, meaning that it will induce higher states of consciousness within the practitioner. The practice is also known as bhrumadhya drishti; bhru means 'eyebrow center' and drishti means 'gazing', hence this is the practice of eyebrow center gazing.
Jay Shiv Shakti