'Pity' might not be a perfect word here since that word makes us think of feeling sorry for someone. They didn't need pity, they needed help. Most often - even in the next chapter - this Greek word is translated as 'mercy'. They needed mercy because they were without hope.
Their cry to Jesus is prayer, desperate prayer. Desperate prayer is a realization in my soul that I am without hope without Him... unless he comes... unless He shows mercy on me... unless He provides what I need.... I need Him. I am desperate for Him. In the next chapter in Luke, we also learn that this type of prayer - persistent, shameless, desperately asking Him to change our lives, our families, our friends, our enemies, our nations, our world - is act of faith.
Jesus tells them to go to the Priest. Lev. 14 says they are to go when they are healed so they can be declared clean. But they were not clean yet. It was along the way that they were healed. This is action. This is obedience. Like desperate prayer, this kind of obedience is shameless. I mean what if they went and were never healed? They would have looked rather foolish. This is also faith. Without being healed yet, they left obeying Him and believing that He would heal them. And He did even from a distance. Faith is taking God at his word. Faith is unseen. It is believing that my circumstances are not reality; to believe who God is, what He is able to do and acting on that faith.
Of the ten that were healed, one - a Samaritan, a foreigner - returned and fell at Jesus' feet, thanking Him and with a loud voice praised God. This worship. This is thankfulness. This is gratitude. And like the prayer and obedience, it is also faith. It is faith because it says again that I believe that God did this and I am overwhelmed with gratitude at who He is. Falling at his feet. Crying out in joy. Shameless thanksgiving. It is a heart that says, I know I was desperate, I am desperate, and I need Jesus. I am grateful for what He has done because of his great love and power. I am acknowledging that he alone is worthy of my worship. Jesus said that his faith made him well. That word well in the original Greek is most often translated 'saved'. (Like in Ephesians 2:8-9, "it is by grace that you are saved...") It is this faith that saved him. It is this kind of faith that saves us and is saving us.
I want to be like the one who returned. I want to see myself as a leper - desperate -crying out to Him in faith, obeying Him even when it looks foolish, returning to thank and worship Him.