By controlling the breath you are controlling consciousness, and by controlling consciousness you bring rhythm to the breath. Like camphor becoming one with the flame, the mind gets absorbed in the flame of the soul. This is the culmination of hatha-yoga. The text tell us that union of the mind with the soul is hatha-yoga. Raja-yoga is also the union of the mind with the soul, so there is no difference between the two.
Yoga is one.
To practice yoga is thus to unite the body with the mind. For the cultured person it is also to unite the mind with the intelligence and for the still more highly cultured person it is to unite the body, mind and intelligence with the depth of the soul. Yoga is traditionally divided into eight limbs or aspects, called yama, niyama, asana, pranayama, pratyahara, dharana, dhyana and samadhi. If you are not familiar with these terms, this long list may seem rather daunting at first. In the course of concepts and the Sanskrit words will not be a barrier to your understanding.