In the first stage we worked on calming the mind through focusing on the out-breath, which is intimately connected with a sense of letting go.
The second stage helps bring more energy and awareness into our relaxed mind by focusing our attention on the in-breath, which is inseparably linked to alertness.
The third stage, in which we pay attention equally to the in- and out-breaths blends these two qualities, of alertness and calmness to help us develop a calm, energetic awareness. When our mind is like this (and you may not have got there yet but it will come with practice) it is very “pliable.” In other words our mind has become a very powerful tool.
What we do with this tool in the fourth stage is to develop one-pointed awareness. This isn’t a forced concentration, but rather a natural absorption that is based on interest and even fascination.
Why is concentration so important? Well, that’s another story. But you can find out more by following another link.