Kriya is a Sanskrit word which means action, kriya yoga intends to that which a person practices can lead a person to yoga aarudhaha (establish in the path of yoga) the ultimate union with universal self. Kriya is the path one has to follow in the day today life, kriya yoga and karma yoga has similar meaning in Yogic tradition . Your life is a chain of actions, either its mental action, verbal action or physical action. Human being has the special faculty of thinking with which he can do an action, not do an action or do an action differently. The freedom of human being is the ability to do actions independently, but the result upon which the freedom is nil nor human being can escape from without doing actions. Lord Krishna accept this in the Bhagavad Gita that the result of each action is governed by the universal laws, the law of karma and law of Dharma is one and the same in Hindu culture, Lord Krishna says "ma bhaleshu kadachana " the result of actions upon which you no control, it indicates the importance of your actions, the freedom one can better choose before doing actions. Your actions lead you to yoga, actions should be done in such a way that one can smoothly travel to the path of yoga.
Great sage Maharshi Patanjali in his yoga Sutras elaborated kriya yoga as "tapas swadhyaya iswarapranidhaanani kriyayogaha " tapas literally means austerity, swadhyaya is self study and iswarapranidhana is self surrender to the lord, these three constitutes Kriya yoga. Kriya yoga is the practical way and a very important step in the path of self realization. These three elaborated a life style in a person who wish to travel his inner journey to perfection. The practical steps one has to follow in actions and inactions, the confusion born out of lack of discriminative knowledge leads to wrong actions and wrong conclusions. The realized sage emphasis a cognitive change in ones perceptions and actions so that one can smoothly sail the samsara sagara ( ocean of worldly life).
The Sanskrit word Tap or tapas literally means "to blaze, to burn, to shine" intended meaning a determined and fully focused effort despite the difficulties to fulfill ones task, to suffer willfully the pain in the the path of reaching a goal, bearing the hot and cold, physical and mental extremes sufferings and hardships in the path of once dedicated goal.
An action performed with a determination and dispassion to a desired result, keeping a strong will to achieve the goal at any amount of effort if needed. A student gets up early morning and engaged in the study in order to achieve a better academic result hoping a better carrier is a simple example of tapas. Yogis doing physical penance and austerity to lighten the body and strengthen the mind. Continued undistracted practice needed to establish in a yoga, stability in asana, pranayama, dhyana all needed relentless effort. Yogis invest there whole life in different forms of austerity is what's the real tapas in yogic tradition. A Sadhaka is suppose to go through and highly disciplined life style in yogic tradition to establish in the path of yoga. It's said in the yogic tradition a beginner has to do at lest twelve years relentless effort to establish in the path of yoga. One has to do tapas at physical, verbal and mental levels in order to rooted in yoga. In the Bhagavad Gita Lord Krishnan teaches Arjuna the meaning of tapas as " worship of the gods, realized souls, the teachers and wise; purity, straightforwardness, celibacy and non injury" constitutes austerity of the body.
The supreme knowledge of yoga can takes place in a very subtle mind only, our mind must be pure, so too body, mind and body is inseparable and one entry, this most sophisticated human body is in every way complete, even then its mis understood and looked upon as incomplete due to ignorance. Atma ( consciousness) is the source of the mind and senses, every cognition and perception is possible because of the consciousness and which itself is causeless and self existing. The Shastras says, even the wise men also is confused in the interpretation of the Atma and its manifestations. At a is not available for any cognition and perception, but every perception, cognition or actions is possible because of atma. The great Vedic tradition delineate a disciplined life so that a person can see the truth in oneself, human intellect alone is capable of this knowledge, knowing this atma, which is the cause of the whole Universe is inseparable from ones inner self.
All distractions of the human mind is it's engagement with the senses, the sadhana is for gaining stability of the senses and mind, from different perspectives one has to work on it, so we have different kinds of sadhana. Lord Krishna is the greatest teacher of yoga said in Bhagavad Gita that one has to give at most attention in speaking, in verbal communication one has to observe tapas ( austerity) Lord further says" speech which causes no excitement, and is truthful, pleasant and beneficial, and the practice of the study of the Vedas, constitute the austerity of speech " if any one can practice this one, ones life would be a great accomplishment for that person, though it looks difficult,any thing comes with difficul effort is always regarded as the best.
In Vedic culture ones spoken words have so much significance and are more valuable than a deed. The adhisthanadevata( presiding deity) of the sense of speech is agni ( fire), that's the reason verbal arguments become hot. More over in Vedic tradition one has to observe certain self disciplines even while saying the truth also , it's said in the tradition if the truth is unpleasant or hurtful one should refrain from saying it. Reciting the Veda mantra is considered as one important verbal austerity, there are numerous appreciationery hymns we may be able to find in all vedas glorifying His manifold manifestations. The first manta of the first Veda ( Rig Veda ) itself commence with the word agni ( fire) , fire is worshipped since time immemorial in ancient Vedic Indian culture. The Sun is the very source of all energy and the Sun the life giving force on earth is worshipped since ancient times, all life forms are possible because of the Sun, we may also find there numerous hymns to glorify the lord Sun in the vedas.
Reciting Vedic mantra is a verbal austerity, all the five elements (space,air,fire,water and earth) are worshipped in Vedic culture , it's said these elements constitutes this whole universe. Veda is the first written record of the human civilization and commanded the highest respect in Hindu tradition, Vedic statements are considered as the ultimate truth both for verifiable and non verifiable facts in Hindu tradition. The three realms of austerity, physical ,verbal and mental, is an important part of spiritual sadhana, while teaching Arjuna Krishnan says " serenity of mind, good heartedness, silence, purity of nature" are mental austerity. We have to cultivate a mind which is suitable for the spiritual sadhana, is austerity. Human mind is the most powerful weapon, which one has to learn to use it properly is the main teaching of the scriptures, mind is the boss of all senses, reason is the guide of the mind. A serene mind is the greatest asset one can achieve by yogic discipline, one has to pay attention to the thought process, we spend more energy in thinking than other functions of the inner organs, mental energy to be conserved and preserved for sharpening the mind training it to see the deeper mind in oneself. Most people in the world are using only the surface of the mind consuming more energy and gaining less from the wold. Even in material achievements also if one apply a deeper mind one can achieve greater results with accuracy and perfection. Mind has no existence other than thoughts, these thought process one can divert to a bigger and more meaningful direction if one practices yogic disciplines. Observing Mauna (Silence) is an important part of yoga sadhana, between two thoughts there is a vacuum, this is the sama sthithi ( equal state) , by practice one has to expand this thoughtless state or samadhi. In samadhi state the mind is at perfect equilibrium, a sadhaka attain tranquility and perfection, this is the yogic state of mind, in all others mind always running out or restless.
Swadhyaya means self study , ones own effort in various disciplines of kriyas envisaged in the Shastras, in ancient times the pupils stayed with the teacher in his home and study . Listening to the Shastras from the teacher is important part of the study and considered it as swadhyaya, more over one has to recite ones own Vedas, daily prayer , chanting, japa ( repetition of the Guru mantra) brought the mind into oneself is the one important motto of japa , during the japa one has engage oneself with meaning of what one is chanting and keeping the mind totally engaged in it is very important. Usually mind engaged in different thoughts, japa could arrest this thinking process and brought it ones own control. Integration of all the scattered mental activity into one field is possible through the japa, more over chanting itself is a considered as punya karma ( graceful action) , each japa is to intended for appreciating the god or goddess. It's believed that the grace of the chanting removes the obstacles in the path of yoga. Vocal repetition of the Shastras is Avery important part of yoga sadhana listed as swadhyaya. Great sage Maharshi Patanjali in his yoga Sutras says swadhyaya as " mokshashastraanaamadhyayanam pranavajapo va" swadhyaya is the study of those scriptures that can librate you from the worldly life birth and death also the reciting of Aum. In Buddhism also we can see chanting as a part of their daily sadhana. Hindu Shastras very much emphasis on verbal recitation of the Shastras as a part of yoga sadhana to achieve inner tranquility and serenity.
Iswarapranidhana literally means surrender to the lord, it's a very big thing in the path of yoga , one has to know Iswara first then only one can totally surrender to His feet, this is the reason in Hindu culture they make alter and do worship. We can invoke the all mighty or all pervading Lord in any given form, Lord has no gender, once we invoke the all powerful Lord in a given form then worship it as ones own deity. One has the freedom in our culture to invoke the deity of ones own choice, we don't worship any idols, the invoked is worshiped. You are free to choose your own gods and free to worship the way you love it. It's a very big ritual to invoke the all pervading Lord in a given form. This is the beauty of the Shastras that it gives us varieties of freedom with which one can choose and worship, no other culture in the world has this freedom. The Veda says " iishavaasyamidamsarvam" the whole universe is the manifestation of the Lord alone. In our culture Lord is not believed but Lord is understood. All whatever here, the earth, the Sun , moon and the stars all the elements constitute the whole universe, the Shastras says this the manifestation of the Lord and you are inseparable from Him, the whole study of the Shastras is to know the oneness in duality. This is a long process much comprehensive and munch complex. An ordinary mind cannot understand it, so we have the yogic disciplines to know it, so yoga is the means to self realization or self discovery, the end is already set and the means is given. Once a person is ready the journey starts there. One has to go to the Guru to know and understand the very swaroopa ( nature) of the Iswara, he also teaches the the nature of a jiiva ( individual being ) and jiiveswara ikyam ( the oneness of the two ) all Hindu scriptures and gods teaches the ones of the creation and the creator . The creator is not separate from the creation, like the spider create a web from its own and take it back to itself. Duality is born out of ignorance, in the wake of discriminative knowledge the ignorance about the self disappears, gaining this discriminative knowledge is pivotal in yogic tradition, because no other knowledge can make a person a complete person, this knowledge alone makes a person complete and fully contented. The person who gain and rooted in this knowledge is the fully accomplished person, he don't ask anything more, rooted in ones own self. Kriya yoga is the path to the self realization.