When you know something, you are aware of its existence. When knowing, you are experiencing something with your awareness. You know the colors of the sky, because you are aware of your experience of seeing them.
Yet, how do you know that you are actually experiencing anything? Clearly, there is no way to know for certain that you know anything at all, that your experiential awareness is true beyond your imagining. Perhaps your experience of seeing the colors of the sky was merely an illusion!
You are then left with two choices. On the one hand, you can assume that you are unable to truly know anything, choosing to believe that you know nothing. On the other hand, you can assume that you are able to truly know, at least something.
In either case, to make an assumption is to act with faith, because having faith is simply having a belief without any evidence that the belief describes reality.
If you have faith that you know nothing, you will question everything. If you have faith that you know something, you will trust the experience of your awareness for whatever you put faith in.
So, know that your life is built upon faith, regardless of what you question, what you trust, or what you believe. When you allow yourself to know, you choose to have faith in your awareness, rather than faith in your thoughts.
It is by allowing yourself to know life, rather than just think of life, that you live a life of faith.