There is a part of ourself that is not completely in our mind but neither in our body. This is where our mind and body touch each other and where they can start to play and influence the changing process of each others.
In Vajrayana is called Speech, because like speech it can vibrate out aloud or it can be heard only in the mind.
Outward vibration of speech is a function of the breath, so if we want to get in contact with this medium between mind and body we have to start there.
Breath can be sensed trough hearing and feeling. But when the breath goes very soft and calm it can only be sensed by feeling. So feeling and breathing can never be separated.
When we start to explore the sensation of the breath, its coming, its abiding and its going we can feel the breath in different part of the body, the nostrils, the chest, the abdomen; but if we relax into the contemplation of the sensation of the breath we discover that the very sensation of our body and the sensation of the breath cannot be really separated.
When we approach a yoga system this way, we set into a new territory in which we can discover subtler and subtler inner panoramas within our own body.
One of my teacher always stress about the fact that the Tantric System is a body vehicle, non a mind one like the Sutra System, because everything we experience in this life we experience within this body.
In yogic tradition there is a lot of teachings about energy moving trough channels in different part of the body with different functions, to support healing processes, rejuvenation processes or spiritual realisations.
All this are nothing else than maps, to guide our attention in a contemplation that can only be accessed by feeling our bodies deeply by relying on the sensation of the breath.