2.20 The in-dweller is pure consciousness only, which though pure, sees through the mind and is identified by ego as being only the mind.
Pure consciousness is a level of awareness exists under subconscious symbolism and our sense of identity. Go back and read my blogpost "Map of The Yogic Mind" and you can read about the mind, it’s components and how they interrelate.
Now, how do I describe seeing the mind as something separate from consciousness? Sutra 2.20 states that we identify ourselves with the mind. If you observe your thoughts however, you will gain mastery over them.
In a small way, we are biological computers that are programmed by our will. Normally our will is on cruise control, but we can take the steering wheel of the car when we realize we are in a car.
One of my favorite toys was the transformer Devastator. He was a large robot made up of smaller robots. Hasbro was a bunch of geniuses for getting parents to buy a whole set of toys to get a bigger one. Voltron was the same way. You had to purchase all five lions to make the Defender of the Universe.
Devastator is the mind. He is made up of separate components that form a larger whole. When they components unite, they work as one. By practicing Yoga, we get the four functions of the mind to work in unison.
Now, the thing is, we all know the real force behind Devastator was Megatron. He called all the shots. The Decepticons lost because they could never get their crap together. In order to fully control Devastator, we have to realize that Megatron is the one behind everything, calling the shots. So it goes with the mind and our consciousness.