At this Jesus said, "Were not all ten cleansed? The other nine, where are they?" Luke 17:17, N.E.B.
It is very hard for us fully to understand what it meant to be a leper in the time of Christ. Today leprosy is a disease that can mostly be avoided; if contracted, it can be somewhat successfully treated. But then it was more than a dreaded fatal disease, more than an awful malady that shattered every cherished human contact. Most horribly, leprosy was firmly held to be the judgment of God, His public punishment for sin, the mark of His sure rejection.
Then Jesus came, full of truth about His Father. He longed to show people that His Father does not inflict diseases as punishment for sin. He wanted them to know that all sinners will find forgiveness when they come home to the Father. Were He ever to walk past a leper without healing him, He would be confirming the people's fear that God will not forgive grievous sinners. No wonder the Scriptures indicate that Jesus healed every leper He encountered.
He even healed ten of them at once, there on the borderlands of Galilee. Ten filthy, isolated, begging men--He made them whole and clean, acceptable to their families, publicly innocent. But only one sensed that his healing, though incredible, was not as important as the Healer. And he came back to worship at Jesus' feet.
The last we see of the other nine is their backs, for their eyes are fixed on their freshly made skin as they scamper off to enjoy the benefits. The gift became the end in itself, and they had no time for the Giver! But Jesus didn't "curse" them by making the leprosy return.
Even in this disappointing outcome Jesus was remaining true to His Father. Though forgiveness is freely offered to all, only those who come back and fall at the feet of the Forgiver have entered into life. The others do not have their forgiveness canceled. But that does not matter. They are lost just the same, not because they are unforgiven but because they indulge the gift, ignoring the Forgiver!