Simon the Pharisee had committed a grave error in hospitality, and a serious error in judgment. In those days, when a guest came to your home, you made sure to provide water for him or her to wash their feet, because the journey on foot was often long and hot and dirty, and it was pretty much always made on foot. But Simon had done no such thing for Jesus.
Simon’s intentions were not hospitable; rather he intended to confront Jesus on some minutiae of the Law so as to validate his opinion that Jesus was a charlatan. He judged the woman to be a sinner, and reckoned Jesus guilty of sin by association. But Jesus is about forgiveness. He didn’t care about the woman’s past; he just knew that, presently, she had need of mercy. Her act of love and hospitality, her posture of humility, her sorrow for her sin, all of these made it possible for Jesus to heal her.
But the one who doesn’t think he is in need of healing can never be healed.