Raja yoga translates the royal path also known as Ashtanga – eight limbs.
These are the tools, practices that a Ashtanga yogi would use for self realisation. In brief, the yamas and niyamas are personal and social codes of the yogi, to purify ones’ thoughts, speech, and actions.
It is the preliminary practices in order for the the other limbs to be successful and according to the ancient seeirs, the disciplines are not governed by cast, time, place and circumstances. It is known as the universal principles and can be followed by any sincere practitioner.
In Hatha yoga, the codes are not dropped but the preliminary focus is to balance the energies of mind and body first. By balancing these two energies, a sense of equilibrium will take place, and then the codes will natural come without inner conflicts. Therefore, Hatha is the preliminary to the high practices of Raja yoga.
In essence, raja yoga is the subtle part of the cleansing, it is when the asana aspect is actually referring to the original seated pose, equipoised, and not the dynamic and changing postures known today. It means, one is able to sit comfortably for a very long time. So the pranayama is being practiced, a certain amount of pranayama practice will allow the yogi to experience one withdrawing the senses (pratyahara). With a certain amount of pratyahara practice, the yogi can experience one pointedness (dharana) without difficulty. Clocking in your time of dharana practice, dhyana is eventually achieved i.e. a continuous flow of undisturbed state of meditation. With continuous practice (yoga abhyasa), one is able to enter into the highest states of samadhi. Free from attachments, free from repulsions. Duality does not longer exist, the ability to know the complete oneness of everything is ever so present.
By practicing the yamas and niyamas, the student purifies the mind. By practicing asana, he gets steadiness and firmness of the body. By practicing pranayama, he removes the tossing of the mind and destroys the over active thoughts and dullness – rajas and tamas. By practicing pratyahara, he gets mental strength, peace of mind, and inner life. By practicing dharana, he get one pointed state of mind (ekagrata). By practicing dhyana, he fills the mind with divine thoughts and enters into the natural state of Being – Samadhi.