He cites the 6th chapter of Isaiah, the commissioning of the prophet by Yahweh. In it, Yahweh tells Isaias to close the people's ears and eyes, make them unable to understand, so that they won't be healed. When Isaiah complains to Yahweh "How long?", Yahweh essentially tells him, until there is only a stump remaining, I.e., until the exile.
The same section of Isaiah is used in all four Gospels in the explanation of why people reject the Gospel.
The commissioning of Isaiah is quite harsh. Attempts to explain away Gods part in the "hardening" of hearts is not easy to do based on the original Hebrew text.
The seemingly simple question of the disciples, "Why do you speak tp them in parables?" gets a complex answer because it strikes at the heart of a divine mystery: the interaction of Gods grace and mans free will.
After prayer and research, this struck me as the crux of the parable and it's what I talked about.
I preached on this yesterday at Mass.
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