If it is seen and if it is understood, then life begins to make sense. We begin to be able to see ourselves - this single, unique individual, us, I, me - as a part of the whole, the awesome plan and purpose that God is working out! Then, being able to see God gives direction to our life. So your eye has seen and your ear has heard, and it has entered into your heart the things which God has prepared for those who love Him.
Those three verses prove that we are predisposed by God's calling to see Him. Not only to know His truth, but to know who His servants are, as well. So we can know. We may not know perfectly; but what we know is a great source of comfort, security, hope, and direction.