Those who are interested in yoga, you will find in the authorized books, yoga indriya-saṁyamaḥ: "The aim of yogic power, yogic success, is to control the senses." Our senses in this material world have been described as venomous serpents. Indriya-kāla-sarpa-paṭala. Kāla-sarpa, cobra, black cobra. So these indriyas are like that. Indriya means senses. As soon as touches, immediately it makes him poisonous. And that is the cause of our material conditional life. The more we are indulging unrestrictedly in sense gratification, we are becoming more and more entangled.
Therefore those who are very much addicted to the bodily necessities of life, for them this haṭha-yoga system . . . haṭha-yoga system means yama, niyama, aṣṭāṅga-yoga. It is called aṣṭāṅga-yoga. Yama, niyama, āsana, prāṇāyāma, dhyāna, dhāraṇā, pratyāhāra, samādhi. These things are in the aṣṭāṅga-yoga. The first thing is yama-niyama. One must have regulated life. That is called yama-niyama. Then practice āsana. There is mechanical process of sitting which will help you, concentration of the mind, āsana. Then praṇāyāma, concentration of the mind. Then meditation.
So meditation is not so easy thing. Unless you practice the preliminary necessities of meditation, you cannot concentrate. Even if you sit down closing your eyes, either you will sleep or you will think of other things which are more important, you think, more important in your life. So the yoga system is practically not very helpful. Helpful means we cannot execute this system very nicely.