Do you think that those people who asked Jesus to heal them in the Gospels should have kept quiet? If Jesus wanted to heal them, he would know their need and respond if he chose to. But the fact is that Jesus told us to ask for what we need (cf. Mk 11:24, Lk 18:1). He obviously wanted those people to express their confidence in his power and love. So it is with us. It is not a matter of trying to change God’s mind. God may very well intend to heal certain sick persons if they ask him to. The prayer of petition requires faith. It is good for us, and he always wants what is good for us.