Yoga Sutra 1.3 is a continuation of what happens after the mind settles down. We begin to see clearly.
The Seer is another way of referring to ourselves in pure consciousness (unchanging, unconditioned awareness). Pure consciousness happens when all traces of ignorance vanish. What is experienced is your Self as pure, eternal, and with unbounded awareness. Like a wave that experiences that it is now, was, and always will be one with the ocean.
How would you see yourself if your inner vision was unobstructed? Peace and bliss are our intrinsic nature. Once the mind is clear we can see this true nature. Our practice helps us clear the path toward this realization: material objects and circumstances in this world aren't good or bad they are neutral - they just are. It is our attitude toward them that make it appear either positive or negative.
Once the Seer realizes this the mind finds no reason to be agitated. We are no longer effected by the charms and temptations of the world.