Breath is important in so many types of meditation because it's the one automatic process in our body we can control. As such, it serves as a little window into our subconscious.
You can't manually beat your heart by thinking about it, but breath is different. You can control it, but most of the time, we don't have to think about it.
Just asking the question "how fast am I breathing?" is enough to change your awareness.
And awareness is always the first step to change.
Every breath we take
Is a prayer.
A sort of quiet yearning
For the rapture we feel
When a warm breeze
On a cool summer night
Fills our lungs
This is the only moment.