Why couldn't the Pharisees understand what Jesus was saying?
Jesus said they could not understand His speech because they could not hear His word. He identified their father as the devil, not God. They rejected His virgin birth and divine origin, accusing Him of fornication, so they did not love Him or receive His words.
Les explains that when Jesus told the Pharisees they do the deeds of their father, they retorted that they were not born of fornication and had one Father, even God. They did not believe in His virgin birth, and the story going through Nazareth was that Mary and Joseph had conceived out of wedlock, or that Joseph was not even the father. Jesus answered that if God were their Father, they would love Him, for He proceeded forth and came from God; He did not come of Himself, but God sent Him. He asked why they did not understand His speech, and answered that they could not hear His word. Les emphasizes that these people were so low, and Jesus then said they were of their father, the devil. So they could not understand because their hearts were not of God but of the devil, and they rejected His word.