I think uncertainty is a gift when dealing with God's promises of healing. If you had told Abraham the day after he received the promise from God that he would have to wait 25 years to see its fulfillment, he might have given up then and there. I probably would have as well. I think that's part of the secret of enduring faith. No one has the faith at one time to wait 25 years for a promise… but anyone can make it one more day.
Let's check out what Jesus has to say about this.
In the Sermon on the Mount, Jesus articulates one of the most beautiful polemics against worry ever uttered. "If that is how God clothes the flowers of the fields, will he not even more clothe you?" He finishes the section with an interesting twist. "Therefore do not worry about tomorrow, for tomorrow will worry about itself. Each day has enough trouble of its own."
Now let's pick things apart and learn a few things. Firstly, notice the imperative nature. This is a command straight from our Lord Jesus. He does not say it is optional; nor does he only say certain people are affected. This is for everyone. Second, we are not giving tomorrow enough credit. Jesus claims that tomorrow will worry about itself. He talks as if tomorrow is an entity which is actively taking care of its own affairs. Thirdly, notice the limiting of the range of focus. We are so apt to try to handle our life at weeks or months at a time. In Jesus' mind, we are biting off much more than we can chew. He is telling us that each day is plenty for our minds to try to digest at once.
I think this is the secret of enduring faith. It's that Abraham made it through 25 years of waiting with his faith intact because he did it one day at a time. No one can believe for healing years at a time, but anyone can keep faith for one more day