Hear, you deaf,
and look, you blind, that you may see!
Who is blind but my servant,
or deaf as my messenger whom I send?
Who is blind as my dedicated one,
or blind as the servant of the LORD?
He sees many things, but does not observe them;
his ears are open, but he does not hear.

Isaiah 42:18-20

The state of being spiritually blind and deaf is certainly worse than suffering from physical blindness or deafness, because it usually develops over a long period of time of ignoring God’s voice found in His word. A.W. Tozer used the word “self-righteousness ” to describe the state of a hardened heart.

Self-righteousness can lead to a blindness to one’s own sin and a lack of concern for spiritual growth, ultimately resulting in a rejection of God’s conviction. – A.W. Tozer

Jesus spoke in parables to the people of his day. Many, especially the religious elites, failed to comprehend Jesus teachings, but it wasn’t that the LORD caused their spiritual blindness, it was their own rejection that caused their hearts to grow calloused. Even though they knew the Scriptures they refused to listen. They refused to see.

This is why I speak to them in parables, because seeing they do not see, and hearing they do not hear, nor do they understand. Indeed, in their case the prophecy of Isaiah is fulfilled that says:
“‘“You will indeed hear but never understand,
and you will indeed see but never perceive.”
For this people’s heart has grown dull,
and with their ears they can barely hear,
and their eyes they have closed,
lest they should see with their eyes
and hear with their ears
and understand with their heart
and turn, and I would heal them.’
But blessed are your eyes, for they see, and your ears, for they hear.

Matthew 13:13-16

How do we avoid a calloused heart, blind eyes and deaf ears? I remember a passage from Proverbs –

Above all else, guard your heart,
    for everything you do flows from it.
Keep your mouth free of perversity;
    keep corrupt talk far from your lips.
Let your eyes look straight ahead;
    fix your gaze directly before you.
Give careful thought to the^[c] paths for your feet
    and be steadfast in all your ways.
 Do not turn to the right or the left;
    keep your foot from evil.

Proverbs 4:23-27