From Dr. Chi's point of view the purpose of t'ai chi is to forget self and become one with the tao.
What does it mean to 'forget self'? When you have a feeling of self your mind already has the idea of separation because as soon as you have 'self' you have 'other'. Also from the sense of self comes 'me' and 'mine' and grasping. The significance of this is far reaching. It affects all experiences on all levels whether emotional, physical or spiritual. The easiest way to begin to understand its importance is from consideration of its martial significance.
In t'ai chi it is important to be able to detect your partner's force. Ordinary strength is easy to detect whereas t'ai chi forces are very difficult to read. So the responses of a t'ai chi master to the attack of an adversary depend very much upon being able to read the responses of the attacker at a vey early stage. This relies on sensitivity which in turn relies on the ability of the t'ai chi master to be able to forget self and become one with the opponent.
There must be awareness of the adversary's intention and the way that the force is gathered or stored. For example, a person may shift weight and gather force from the opposite foot with the intention of lifting the other foot to kick. When the force begins to manifest, the response must already be attuned to the direction and weight of the issuing force so that the response can be well timed. To achieve this level of connection with an adversary the master must have a very quiet mind, free of all emotional disturbance. He or she must be able to let go of the distinction between 'self' and 'other.'
It is very much a feature of the mental aspect of t'ai chi that a person is able to loosen the hard and fast distinctions that are perceived between one thing and another. To make this clear consider the boundary that one experiences in relation to one's own skin. What is seen is a clear visual boundary. Look at your hand. The edges are clear to see. Close your eyes. Ask yourself where does your hand finish and the air begin? It is not so clear.
In the same way feel your feet. Where do your feet end and the ground begin?
These distinctions are similar to the the distinctions we experience when we consider 'self' and 'other.' It is our thinking mind which keeps them separate. Also if you think about the terms themselves they only have meaning in relation to each other. To you I am 'other.'