Jesus is speaking to a paralyzed man. (This is the one who was lowered through the roof into the room where Jesus is speaking.)
When we come before our Savior, we come looking for forgiveness. We speak to Jesus about healing, but it is the fate of our souls which bring us to him. I am prepared in every instance to proclaim "the forgiveness of sin," but I pause when asked to pray for the curing of disease. (This is a confession - not an instruction.)
There are many sophisticated reasons why I (and perhaps you) respond in this way. But we need to occasionally admit that we focus on only part of the story. Jesus does heal.
I don't know why Jesus doesn't heal every infirmity. And I am careful not to put God to the test by asking for healing. But scripture is clear about this - and what I can say without hesitation is that God wants what is best for us.
When you share with me the need you have for healing, trust that I sat aside my sophisticated theology and answers about why bad things happen in the world and go directly to God to ask for restoration. I may not have an answer to give in the classroom, but in my prayer chamber there is one - I present to God the needs of God's children and I ask God to attend to them.