Mark 4:9-12 (NASB): “… ‘He who has ears to hear, let him hear.’ And as soon as He was alone, His followers, along with the twelve, began asking Him about the parables… ‘To you has been given the mystery of the kingdom of God; but those who are outside get everything in parables, in order that while seeing, they may see and not perceive; and while hearing, they may hear and not understand lest they return again and be forgiven.’ ” (See also Matthew 13:10-15.)
Verse 12 is a quotation from Isaiah 6:9-10. God instructed Isaiah to tell Israel that because they would not hear and obey Him, they would be cast off from God’s favor. Israel was blind to God’s providences and laws. They followed other gods and other people’s customs. Therefore, they would no longer receive His favor.
The Apostle Paul also preached with this Isaiah passage in Romans 11:8. He said that Israel’s failure to accept Jesus as their Messiah was prophesied. This explained why the message of salvation went out to the Gentiles. Israel as a nation lost the privilege of the heavenly promise (although individual Jews did become followers and disciples).
Jewish thinking was so set on doing works under their Law Covenant that most of them failed to see and understand the message of Jesus, that we are to live according to the spirit of God’s Law. It involves a change within our hearts.
Therefore, the text of Isaiah that Jesus quoted was directed specifically to his Jewish audience. Was Israel to be cast off forever? No! In the last verse of Isaiah 6, there is reference to a stump of a tree left in the ground. The implication is that at a later time, it would sprout again—favor would return to Israel. Today, Israel has been reestablished as a nation!
Furthermore, the promise continues in Romans 11:26-32 (NIV): “And so all Israel will be saved, as it is written: ‘The deliverer will come from Zion; he will turn godlessness away from Jacob. And this is my covenant with them when I take away their sins.’ … they too have now become disobedient in order that they too may now receive mercy as a result of God's mercy to you. For God has bound all men over to disobedience so that he may have mercy on them all.”