They did not have the ability to hear because they were not of God
In John 8:13 we know this conversation was between Christ and the Pharisees.
This must be established to understand what is being said to who.
Christ tells them they are of their father the devil.
Then tells them they will not believe the truth because they are not of God.
BF, this means they did not desire the truth of God, they did not covet the things of God, they only cared for their position and power ofver the people.
They could not hear the truth because they had their own truth.