God cursed His people Israel with blindness [Isa 6:8-13].
This isn’t an Old Testament phenomenon, but the nature of God.
The same curse is repeated by Jesus in the New Testament [Mat 13:3-17].
Jesus used parables when speaking to those who were not granted understanding of the Kingdom's secrets, as they were not meant to receive this knowledge [Mat 13:11].
The purpose of parables is to conceal the message from outsiders.
Jesus said those who have will be given more, and those who don’t have, will have what little they do taken from them [Mat 13:12-15].
This means that the curse of blindness is a punishment for specific people, not the entire nations. The curse is conditional
The curse is punishment for the people closing their eyes [Mat 3:15].
If they turn from closing their eyes, the curse would be lifted [Mat 3:15].
To “hear” the parable is to understand it [Mat 13:18 KJV].
Jesus Christ was telling them they were doomed in a way they didn’t understand. It’s like a doctor telling a patient he is sick, but using words that the sick person can’t understand.
This goes to show the sternness of God. He is not as sentimental as people lie He is.
God said He would mock His people for failing to pay attention to Him. This is an example of a fulfilment [Pro 1:22-33; Ezek 14:1-7].
God calls such people simple, mockers, and fools [Pro 1:22].
He says that when they call to Him, He will not answer them [Pro 1:28].
Animals pray to God [Job 38:39-41].
Demons pray to and worship God [Mar 5:1-15].
The demons prayed Jesus to swear to not to torment them [Mar 5:7].
They prayed that He shouldn’t send them out of the country [Mar 5:10].
They made the prayer more specific by asking He send them into the swine [Mar 5:12].
God places good and evil before us and asks us to choose life [Deu 30:19].
If you choose darkness, heaven will oblige – as has been demonstrated above – and help you stay in darkness – in this case, by worsening the blindness
God speaks of His blind and deaf servants. He says they don’t see, because they don’t pay attention [Isa 42:19-20]