The requirements for knowledge / belief in science are far different than those required in religion. Scientists are very careful with their use of the terms "to know" and "to believe" -- and the word "faith" is anathema. Religion has no such strict interpretations and often use the three terms interchangeably.
It only took me a semester of biology to have a problem with my preacher saying things like, "Know this, when you die, you'll either go to Heaven or Hell". Well alrighty, then! OK, you might scare me into one or tempt me into the other, but you can't make me "know" that I'll land in either one. Then he would ask me if I "believed" this. Of course I said yes, rationalizing my surrender by letting the word "believe" dilute "know" down enough to be palatable.
But that didn't fix the dissonance in my mind. It only grew worse the farther I got into science. Common origin, natural selection, speciation, genetics, geology -- on and on -- contradicted almost every thing I had been conditioned to believe. I finally came to the conclusion that I had to make a choice. I had to dump either science or religion. I dumped religion. At least I tried damn hard to. But the dissonance remained -- until a few years ago. So what cleared things up? My definitions of the words "knowledge", "belief" and "faith". Here they are.
- Knowledge requires empirical, non-disputable evidence. Example: Neil Armstrong knew he walked on the moon on July 20, 1969. I can't know this, but he did.
- Belief requires objective evidence that can be proven beyond a reasonable doubt. Example: Objective evidence supports Armstrong's walk on the moon. I have no choice but to go where the evidence takes me.
- Faith is based upon hope and does not require a minimum amount of evidence. Of course, to have hope usually requires some amount of evidence, but it can be entirely subjective. Example: Having faith that on August 25, 2012, Neil Armstrong became an astronaut in God's space program, regardless of the lack of objective evidence. (I can have faith in this if I so choose, but I cannot know or believe it.)
Thus, I'm at peace. As long as there is the unknown, I can choose to hope for anything I want, even if the only evidence I have is almost 100% subjective. I call it “faith”. It's my choice. I can have “faith” in Heaven even if I don't have enough evidence to know or believe in it. However, I don't need faith to accept evolution. I have sufficient objective evidence. See? No more dissonance.