In both Matthew 13:14 & Mark 4:12 Jesus is quoting this Scripture from the prophet Isaiah to explain why He spoke in Parables. Those who had already rejected Him didn’t have divinely enlightened minds in which to perceive spiritual truths – and no amount of explanation would make them understand. (I Corinthians 2:14) They could only watch & hear Jesus with their physical eyes & ears…not capable of understanding the truth He spoke about…their hearts hardened because of rebellion, pride, and self-will. (II Corinthians 4:3-4) But to those who had not hardened their hearts and were instead obedient & submissive, the Parables revealed, as Paul wrote in Ephesians 3:4 & Colossians 4:3, the Mysteries of Christ. So, “Today, if you hear His voice, don’t harden your hearts…” (Psalm 95:7)