The breathing exercise of the yoga system that is generally practiced is just the beginning of the system. Meditation on the Supersoul is just a step forward. Achievement of wonderful material success is also only a step forward. But to attain direct contact with the Supersoul and to take dictation from Him is the highest perfectional stage.
The breathing exercises and meditational practices of yoga are very difficult in this age. They were difficult even five thousand years ago, or else Arjuna would not have rejected the proposal of Krishna. This age of Kali is called a fallen age. At the present moment, people in general are short-living and very slow in understanding self-realization, or spiritual life. They are mostly unfortunate, and as such, if someone is a little bit interested in self-realization, he is misguided by so many frauds.
In the present age, however, if you want success in practical yoga, take to the chanting of Hare Krishna, Hare Krishna, Krishna Krishna, Hare Hare/ Hare Rama, Hare Rama, Rama Rama, Hare Hare, and feel for yourself how you are making progress. Lord Chaitanya practically demonstrated Krishna consciousness yoga simply by chanting the holy names of Krishna, as they are mentioned in the Vedanta, the Srimad-Bhagavatam, and many important Puranas.It is very easy and practical for this age, especially for those who are serious about success in yoga. No other process can be successful in this age.
Ref : Chapter 5a, Science of Self Realization authored by Srila Prabhupada (Founder – Acharya, ISKCON)