To someone who inquired about the nature of authentic Raja Yoga.
Raja Yoga is the science of Prana, the breath being the main yogic instrument for its accomplishment. It is much more than controlling or refining the breath (for real pranayama is refinement, not control), it is the Way of Unity.
Raja Yoga both leads to and is the experience of unity with the Self and Brahman. Total unity is its only goal. This is important to recognize, because Raja Yoga involves mastery of our inner and outer life, which inevitably involves the emergence of inner powers which can easily be wasted or misapplied.
Raja Yoga and yoga powers (siddhis)
It is pointless to tell a yogi to “shun the yoga powers” any more than it would be to tell a child to avoid adulthood. Certainly, an adult is subject to many more delusions and addictions than a child, and certainly has the ability to work much more harm to himself and others. Nevertheless, adulthood is inevitable.
And so it is with the yogi: these powers will manifest in him. If he keeps his eye upon the goal of liberation in Brahman, those powers will ripen into something more, into spiritual realizations, much the same way that sexual energies conserved are transmuted into far higher and greater forces within the consciousness of the yogi.