John 12:37-40 But though he had done so many miracles before them, yet they believed not on him: That the saying of Esaias the prophet might be fulfilled, which he spake, Lord, who hath believed our report? and to whom hath the arm of the Lord been revealed? Therefore they could not believe, because that Esaias said again, He hath blinded their eyes, and hardened their heart; that they should not see with [their] eyes, nor understand with [their] heart, and be converted, and I should heal them.
Just like these with Paul who could not understand like Paul who was called and heard and followed.
And the men which journeyed with him stood speechless, hearing a voice, but seeing no man. Acts 9:7 And they that were with me saw indeed the light, and were afraid; but they heard (understood) not the voice of him that spake to me. Acts 22:9
They were not called and even though hearing their ears were not opened to understanding.
Scripture is clear that God does harden hearts and blind those who have chosen to reject Him over and over. This does not mean everyone's heart is hardened by God.