The four realities in your life are - body, mind, emotion and energy. The four paths of yoga are around these four realities of your existence. If you use your emotions to reach your ultimate nature, that is bhakti yoga. If you use your mind, that is gnana yoga. If you use your body, physical action, that is karma yoga. And if you use your energies, that is kriya yoga. On a spiritual path, why so much significance is given to a live guru, is because, he can mix these in the right proportion for you. What works for one person, may not work for the other. These four dimensions have to work together.
Karma Yoga has been misunderstood as service. It is not that. Yoga does not need karma, yoga is to go beyond karma. But right now, you need some activity - that is why the crutch of karma yoga. It is needed to manage your awareness. Karma yoga is to joyfully involve yourself in any activity. Sadhguru says - "To do something which does not mean anything to you but with total involvement is what breaks the karmic structure".
Sadhguru says, in the state you are right now, there is still need for action. Someone who doesn't know intense action, can not move into inaction. So, choose the action that you want to do - either to rule the world, or to serve the world. And do it with absolute intensity. Sadhguru narrates a beautiful story of a Zen master - "No Work, No Food".
Kriya means internal action. So, it is not on the level of your body and mind, it is on the level of your energies. Body, and mind are not reliable - they can be influenced easily. But, when you work on your energies, you will experience a different depth to life. Kriya yoga is a very powerful way, but also very demanding. It is not for those who are constantly seeking comfort. Kriya yoga is a path for those who want to do things beyond realization. This is for those who want to know the mechanics of life making.
Sadhguru tells us that kriya means internal action, sound or music is an external action. So, for most people, sound or music is karma not kriya. But music can be transformed into kriya. It depends on the quality of the listener. If one's listening becomes very keen, then the listening is not just limited to the eardrums, every cell in the body can reverberate. Sadhguru says - "If your whole body can listen, what is just entertainment can become kriya yoga for sure."
Gnana means "to know". To pursue gnana yoga, you must have a very sharp and alert intellect. It should be razor sharp, to a point where it does not miss anything, but it is not influenced by anything happening around it. Sadhguru says - “What I know, I know. What I do not know, I do not know.” This is gnana.
Intellect is a wonderful faculty of a human being, and is absolutely essential for survival. A gnana yogi, begins by using his intellect, and ultimately realizes it's limitations. Unfortunately in contemporary societies, intellect has been granted a disproportionately large significance. A gnana yogi, realizes that intellect is of no use when it comes to the mystical dimensions. Sadhguru says - "Gradually, those on the gnana yoga path learn to access the deepest dimension of human intelligence, which connects them with the very basis of creation. This realm is known as chitta."
Sadhguru says, that there was a time when emotion was the most dominant part of a human being. It is not so now, but still it is the most intense part. People can not sustain intensity in their body, mind or energies. But emotions can get very intense. Bhakti yoga uses the intensity of emotion to reach the ultimate. Bhakti yoga, or devotion, is a multiplied or enhanced form of love affair. Sadhguru says, you can not practice devotion, but one can do certain things to naturally become a devotee.
Sadhguru says that devotion is like having a love affair with the creation. What people usually call love, is not love, but discrimination. Because they love one person and hate another. "Whether it is a tree, an insect, a bird, an animal, a man, a woman, or a child – learn to look at everything the same way. Without transcending this discriminatory mind, without establishing a non-discriminatory way of looking at everything, you will never be a yogi".