When we are able to effectively unify dharana, dhyana and samadhi we acquire super human powers or ashtama sidhhi. Dharana is an advanced stage of concentration. Normally we talk about concentration on studies, concentration on our work etc. But dharana is beyond concentration. We concentrate on something that exists. When we say concentration on studies, we talk about a study that is the subject matter here. When we concentrate on a burning lamp, lamp is the object here. So, in an ordinary level of concentration, there has to be an object or a subject. When we meditate on God, most of us concentrate on a manifested form of God. Dharana is different, wherein we have to concentrate on the thoughtless form of the mind.
Mind is always a culprit and modifies the qualities of man according to its whims and fancies. In this stage we are under the control of mind. In dharana process, we have to detatch mind from any subject or object. This is the initial stage of meditation. The next is dhyana. A good dharana leads to a good dhyana. Dhyana is meditation. As said earlier, you have to have either a subject or an object to meditate. But in dharana there should be no subject or object. Meditating on the outcome of such a dharana is called dhyana.
In this stage, dharana merges with dhyana. What happens when dharana and dhyana merges? Krishna answers this question in Gita. He says that is he is omnipresent and omnipotent and that one should be enlightened with this knowledge of universal existence of God. LS 254 describes this stage as dhyana dhyatru dhyea rupa a situation where there is no difference between the process of meditation, the meditator and the object of meditation. The subject and object of meditation merges here. This dharana and dhyana leads to the next stage called samadhi. In dhyana stage, meditation happens. The samdhi stage is the final stage of ashtanga yoga. The entry point of this stage is the unification of dharana and dhyana.
What is the result of this unification? The result is detachment from involvement in worldly activities. You are not stopping your worldly activities, but you don’t get involved in those activities. Without detaching yourself from your activities or in other words realising that you are not responsible for your activities and the consequent result there to be not yours, you cannot go to this samadhi stage. Samadhi is formed out of two words sama+adhi. Sama means equal. Adhi means the supreme. Samadhi cannot be practiced and it has to happen on its own. It will happen on its own only when you are thorough with the previous seven stages. What is Equal? Your mind and self becomes equal and merges into a single formless form called Brahman.
Then what is supreme? Brahman is the supreme. To understand and realise that Brahman is within us as well, we have struggled through the earlier seven angas or parts or limbs. We finally come to the conclusion “aham brahmasmi” meaning I am that Brahman or I am the God. It means don’t search Brahman elsewhere, realise Him in your own self. This stage is not just identifying us with God but becoming God himself. This is called self realization.