First understand these premises, earthly wisdom and Godly wisdom.
James 3:14-15 (NIV)
14 But if you harbor bitter envy and selfish ambition in your hearts,
do not boast about it or deny the truth. 15 Such “wisdom” does not
come down from heaven but is earthly, unspiritual, demonic.
James 3:17 (NIV)
17 But the wisdom that comes from heaven is first of all pure; then
peace-loving, considerate, submissive, full of mercy and good fruit,
impartial and sincere.
This is the answer to your question
Isaiah was commissioned by God to go and rebuke a wicked people and deliver this curse to them.
Isaiah 6:9-10 NIV
9 He said, “Go and tell this people:
“‘Be ever hearing, but never understanding; be ever seeing, but
never perceiving.’ 10 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.”
Wicked people and the wisdom of this world
God has purposely shut off the understanding of His word to the common man. Because of that mans wickedness he will never know the truth about God. But if that man turns from his wickedness, repents, and has faith in Jesus Christ, then God will open the flood gates of wisdom so that you may understand His word.
They are darkened in their understanding and separated from the life
of God because of the ignorance that is in them due to the hardening
of their hearts.
Children of God
God promises a wealth of understanding when He gives you the Holy Spirit.
that he lavished on us. With all wisdom and understanding,
The Spirit of the LORD will rest on him— the Spirit of wisdom and of
understanding, the Spirit of counsel and of might, the Spirit of the
knowledge and fear of the LORD—
... We continually ask God to fill you with the knowledge
of his will through all the wisdom and understanding that the Spirit