For those who are too engrossed in the bodily conception of life, the yoga system is very good, because it is a practice to withdraw the senses from their engagement in the external world. However, yoga is not so easy. Many so-called yoga teachers are simply exploiting people.
There are eight stages of yoga practice. The first two are Yama and niyama. Under regulative principles, one has to try to control the senses in eating, sleeping, and working. That practice is called Yama-niyama. The first principle of yoga is to abstain from sex life. Those indulging in sex life, intoxication, and so many nonsense things have no chance for any success in yoga.
Then one has to sit nicely in a secluded, sanctified place with the neck, head, and body in a straight line. Then you have to look at the tip of your nose with half-opened eyes. If you open your eyes, then the material manifestation will disturb you. And if you close your eyes, then you nap. Another step in the eightfold yoga system is Dharana, the concentration of the mind. What is the purpose of concentrating the mind? To find me within the body and then find the Lord there, that is the perfection of yoga.
Although yoga is approved in the Vedic literature, it is very difficult to perform in the modern age. Even five thousand years ago – when the circumstances were more favorable, when people were not so polluted and were advanced in so many things – still, at that time such a person as Arjuna refused to practice yoga. When Kṛṣṇa said to him, “You become a yogi like this, “Arjuna said, “It is not possible for me”.
So yoga is not at all possible now. It was possible in the Satya-yuga when every man was in the mode of goodness, every man was highly elevated. Yoga is meant for highly elevated persons, not ordinary persons. But even if yoga is done very nicely and perfectly, it cannot take you to the Supreme Lord. That is stated here in this verse. What to speak of pseudo yoga, even if you perform yoga perfectly, still you cannot reach God. That is stated here: na sadhayati mam yogah.
Source: A.C. Bhaktivedanta Swami Prabhupada (2014 edition), “The Quest for Enlightenment”, Page 95