Before indulging in pursuit of truth seeker has to:-
1 The first step is to rectifying the reasoning base mentally from form to formless.
2 Then analyzing the three states on the base of the formless self/soul/consciousness.
3 Analyzing and discriminating between three states and the formless soul, which is the substance and witness.
Seeker has to learn to view and judge the three states on the base of the soul as self. Seeker has to mentally reject all the religious, yogic, and intellectual theories as they are based on the physical self. This is possible when the he rectifies its reasoning base.
Soul neither rises nor subsides. Soul is formless and non-dual in its nature and it is substance of the mind. Mind rises and subsides is illusion. The substance and witness of the illusion is the soul.
Just as the witness of the dream does not go, anywhere only the dream appears and disappear the waking experience also appears and disappears. It is appears to the formless substance which is the soul and disappears as soul. Therefore, the substance and witness of the mind is soul. Thus the mind and soul are one in essence.
Soul is in the form of sprit or consciousness and it pervades in all the three state. All the three states are illusory on the standpoint of their formless substance. If the soul is in its formless and non-dual true nature then there is no mind and no duality. All the confusions and doubts arise when the three states are viewed on base of physical self. If soul/spirit is not the witness of the three states one would not had the idea of deep sleep and dream in the Waking experience.
When one has the firm conviction that the formless soul is the substance and witness of the three states he renounces them three states mentally by realizing their unreal nature but does not abandon it. And he views them on the standpoint of the soul as self, which clears the fetter created due to viewing on the physical self. Therefore the realization of the truth is right here in this waking experience and right now that is not in next life.