Observing breathing while meditating can be very effective in reducing the number of thoughts because thoughts are mind, and the primary goal of meditation is to go beyond the mind.
But, OBSERVING is a word of significant importance.
Many people think that they have to CONTROL their breathing or FOCUS on their breathing.
Both approaches are incorrect.
Why?
Because meditation is NON-DOING, but our whole life in the world is in DOING ( Do something to get something ).
So, CONTROLLING, FOCUSING, etc., are acts, DOING.
And any DOING expects results.
With such expectations, meditation will not happen.
So, it is essential to just OBSERVE breathing.
But why breathing?
One breath is no different than the other.
So to develop a nonjudgmental attitude, breath becomes an accessible vehicle.
I you observe a picture of God, for example, chances are that you would start thinking about that God, what he did in the world, etc, and thoughts will take you into the mind, from which you are trying ti rise higher.
2. Sansar is full of DUALITY, which requires our attention and requires us to choose based on our likes, dislikes, etc.
It is an unending journey ( till we die ). ( and that’s why we never get the taste of the non-dual ( Advait ) parmatma till we die.
In such a dualistic world – breath is a great avenue to connect to Him because you can’t CHOOSE one breath over another. They keep coming, all exactly the same.
3. The beauty of a breath is, despite being formless, it is short lasting. Each breath has a beginning and an end.
So, despite being formless, it has a flavor of materiality ( form ), which is impermanent.
And the idea of meditation is to rise above whatever is impermanent ( Sansar ) into something permanent ( Godliness ).