Yoga means union, union of the individual soul with God, the Supreme Soul. Yoga also means a way to attain this union. Thus karma-yoga is the means to union with God through selfless work, or work done as worship, bhakti-yoga is the means to this union through devotion, raja-yoga is the means to this union through meditation, and jnana-yoga is the means to this union through knowledge and discrimination.
Swami Vivekananda gave eight illuminating classes on Karma-yoga in New York from December 1895 to January 1896. These lectures deserve to be repeatedly studied and reflected on. He speaks of two kinds of Karma-yoga: work for work's sake and work for God's sake. Work for work's sake is doing work selflessly, without worrying about the existence of God or any other metaphysical doctrine. Swami Vivekananda held Buddha to be the ideal example of this kind of Karma-yoga. However, he makes it clear that doing work for work's sake is not that easy: "Nothing is easier to say, 'I work for work's sake', but nothing is so difficult to attain. I would go twenty miles on my hands and knees to look on the face of the man who can work for work's sake. There is a motive somewhere. If it is not money, it is power. If it is not power, it is gain. Somehow, somewhere, there is a motive power."
Work for God's sake is the way for most spiritual aspirants. It makes spiritual practice easier and more fruitful. Swami Vivekananda explains: "For those who believe in God there is another way, which is much less difficult. They give up the fruits of work unto the Lord; they work and are never attached to the results. Whatever they see, feel, hear, or do, is for Him. For whatever good work we may do, let us not claim any praise or benefit. It is the Lord's; give up the fruits unto Him. Let us stand aside and think that we are only servants obeying the Lord, our Master, and that every impulse for action comes from Him every moment. Whatever thou worshippest, whatever thou perceivest, whatever thou doest, give up all unto Him and be at rest. Let us be at peace, perfect peace, with ourselves, and give up our whole body and mind and everything as an eternal sacrifice unto the Lord. Instead of the sacrifice of pouring oblations into the fire, perform this one great sacrifice day and night-the sacrifice of your little self."
According to Patanjali's Yoga-sutras (2.1), "Kriya-yoga consists in austerity (tapas), study (svadhyaya), and surrender to God (ishvarapranidhana)." Commenting on this aphorism Swami Vivekananda says, "Kriya-yoga literally means work, working towards Yoga." That means doing work as a spiritual practice. The three disciplines mentioned here are vital to the conversion of karma, or mere work, into karma-yoga, or work as spiritual practice. We will study these disciplines one by one.
Tapas, or austerity, is commonly understood to mean physical mortification: standing in prayer in neck-deep water, standing with upraised arms, braving extremes of heat and cold, keeping vigils and observing fasts on auspicious days, giving up a favorite food after visiting a holy place, and so on. These physical practices might have some beneficial effect on the mind, but, says Swami Brahmananda, "Those are not real austerities. Anyone can practice them. The body is easily controlled, but it is another matter to control the mind. It is very difficult to renounce lust and greed, to give up the desire for name and fame."