Why would you need faith if you had no doubt?

This is a general spiritual response, and it's not meant to be Orthodox-anything... although I think people of most religions would probably agree with a lot of it anyway.

Faith is the belief in Divinity, whatever you believe that to be, despite not having any external evidence to back that up at the time. I think you're right, faith is only relevant when you have some reason to doubt. Otherwise it would be knowledge, if you had proof of it. For example, trying to reconcile Religion and Science. If they proved it, it wouldn't be Religion anymore. It would be Science. Faith in a non-spiritual sense would be the faith we have that our significant other loves us very much, even if they don't say it. On second thought, that's probably spiritual after all.

Let's consider what a lot of people believe their Divinity to be. They believe it to be a Perfect, Benevolent, All-Powerful Creator. And the world in which we live gives us a lot of experiences that seem to contradict that notion. Suffering, lovelessness, greed, hypocrisy, environmental damage, species extinction. The experience that we as a world value money as being more important than people, and so a few of us have loaded bank accounts while many more experience poverty and death. All of these things seem to be evidence against the existence of that kind of Divinity. Just being on the planet will cause people to encounter an ongoing barrage of life-experiences that seem to disprove that concept of a Creator who is Perfect, Benevolent, and All-Powerful. Just being here, we encounter one big argument against the existence of that kind of Divine being, and it wears us down. Personally, I think that's the whole underlying purpose of this world - to make an argument for lovelessness despite what we truly are, and to hide the truth where it can. That isn't much of a purpose, I grant you. But then, this isn't much of a world, either.

There's another way of looking at it. My secret is that since this world and my faith clash and there's no resolving them, I discard my belief that this world is real. I didn't have much invested in it anyway. Lots of mystics have said throughout the ages that Space and Time are illusions. Dreams. From what I've seen, I believe them. At that point, none of this absurdity really matters, and the only thing left is to abide in Love.

And that's kind of the whole point anyway.