The later part of Jesus’ statement - "Though seeing, they do not see; though hearing, they do not hear or understand" - is drawn from the book of Isaiah:
Then I heard the voice of the Lord saying, "Whom shall I send? And who will go for us?"One might ask why God is telling His servant Isaiah to make the hearts of people in that society calloused. Why?
And I said, "Here am I. Send me!"
He said, “Go and tell this people: 'Be ever hearing, but never understanding; be ever seeing, but never perceiving.’ Make the heart of this people calloused; make their ears dull and close their eyes. Otherwise they might see with their eyes, hear with their ears, understand with their hearts, and turn and be healed.”
Then I said, For how long, O Lord? And he answered:
“Until the cities lie ruined and without inhabitant, until the houses are left deserted and the fields ruined and ravaged, until the LORD has sent everyone far away and the land is utterly forsaken.” (Isaiah 6:8-12)
This explains that ultimately it is the Supreme Being who allows those who do not hear His message to not hear it: "Make the heart of this people calloused; make their ears dull and close their eyes."
The Supreme Being is simply allowing those who want to be away from Him to remain away from Him. He doesn't want to force Himself upon us.
This is love. Love requires freedom. No one can be forced to love someone. As such, the Supreme Being allows those of us who do not love Him to remain away from Him.
If He didn't, then we couldn't ignore Him very well could we? Because the Supreme Being is God, it is pretty hard to get away from Him. So how does He hide from us?
He has put us within this physical world and given us these physical bodies, which we falsely identify with. These physical bodies allow us to take on false identities in order to pretend that we are someone else for awhile.
This is the illusory energy of the physical world. When we falsely identify with these physical bodies we can think that we are the greatest. We can remain within our self-centeredness and chase the forms and things of the physical world without having to face Him.
While the Supreme Being wants us back, He wants us to decide this for ourselves. Those who make a determined decision to come to know Him and return to Him are given an opportunity to hear from God's representative and be guided back to Him. Those who decide we want to continue evading the Supreme Being and attempt to enjoy ourselves - we are left alone.
And alone is right. This is a lonely venture. Those who are left alone in the physical world - misidentifying ourselves with these physical bodies - are perpetually lonely. We might be surrounded by a big family and lots of friends or adoring fans, but we will still be lonely if we do not have our Best Friend and Sou Mate - the Supreme Being.
This is because the Supreme Being created us for the purpose of loving and serving Him. This is our real identity. But because love requires freedom, He allows us the freedom to choose Him. Those who decide they don't want to assume their real identity as one of God's loving servants and playmates become overwhelmed by self-centeredness. This results in our fall to the physical world.
However, for those who are driven to understand the true meaning of Jesus words: For those who do not care what others think, and have a sincere and humble desire to come to know the Supreme Being as He is, the Supreme Being gives them the understanding to be able to hear the teachings of God's representative.
(For a translation of Jesus' statements from the Book of Matthew without institutional sectarian influence, see the Gospels of Jesus - translated from the original Greek texts.)