We all have periods of doubt. Times when we don't know which way things might turn out and we start to question things about our faith. In the children's movie Polar Express the young boy struggles with his doubt about Santa. He sees the fake ones in the big store window. He keeps coming down from his room to see if he can catch whoever leaves the gifts. Then he gets taken on this journey by a train that appears right on his street.
You can see his doubt as the conductor asks him on the train. Finally he is in the square at the North Pole and Santa has come out. The crowd is so big he can't see him. A bell falls to the ground off a reindeer and he picks it up, rings it and proclaims in all his doubt "I believe."
Belief is mingled with doubt. We believe in someone whom we have never seen, we believe in words written in a book which don't always agree, we believe there is some way to nail down belief and make it explainable. This is not belief. Just like Thomas we want to know concretely that all the promises of Jesus' resurrection are true. We want to be able to touch, make it tangible, make it assured and it is not.
Faith is stepping out on our doubt though and making the journey. Just like the boy decides to get on the train. We decide to take the first steps of faith. I believe, mixed in all the doubt we have.