You know, it is not enough for us Christians, to just want a healing or anything else from God. God wants to see, that we demonstrate our faith somehow. One thing is to believe, but entirely other thing is to act on your faith.
When we read Matthew 8:6,7, we can see, that there is a questions, which Jesus asked the centurion. Now, did not Jesus know, that all that the centurion wanted, is for Jesus to heal his servant. Of course, he knew, because the centurion has already told him so. But despite the fact, that Jesus knew what is the problem with the servant of the centurion, and what that centurion wanted Jesus to do for him, he still asked the centurion that question ‘Shall I come and heal him’? Was that question necessary? Well according to the centurion, probably not, but according to God, yes.
You see, God wants us to not only believe his Word and his promises, but to also act on our faith. God wants us to confess our faith in him and his Word, just like the centurion did, by saying to Jesus, to just say the Word, and his servant would be healed, in verses 8, and 9.
If Jesus did not ask the centurion that question, if he should go to the place of the centurion, and heal his servant, perhaps the centurion would not make those great statements of faith, before Jesus, which he made in verses 8, and 9. What the centurion said in the verses 8 and 9, was pure faith in what Jesus can do for him, pure faith and a confession of faith in the miraculous from God.
That is why Jesus was amazed at his faith, and commented that the faith of the centurion is a great faith.
God could ask us a question, to test our faith, before he gives us a miracle, in order to see our response, if it will be a response of a great faith, which will glorify God, and will bring the miraculous, or it would be a lack of faith, which will be like a handbrake for the miracle from heaven. And all that is left, is up to us, how we want to respond to the promises of God.