It's not a contradiction, you don't understand. Faith is the serious belief that something can happen or is real. When a scientist embarks upon a hypothesis, he does so because he has
faith that something valuable may come from experimenting on that hypothesis, which is a hope for value not yet seen. Faith is not just a belief or hope, but it is a set of works accomplished in the attitude of that hope, so the scientist, by faith, continues his experiments on a hypothesis.
The same process occurs in the spiritual and religious realm with regard to faith. Religious people hear that certain information and/or manifestations are available to them, and they have faith sufficient to follow the path outlined. As they do so, they find their initial faith validated, and then they continue to have faith on the next point outlined in the scriptures, and find that faith validated, and so on.
Faith is not knowledge; faith is a stopgap on the way to knowledge, and it's a principle necessary for healthy or reasonable conduct in all forms, which is part of why religion requires such an emphasis of faith. If a man obtains all knowledge, there is no more need for faith, because he knows everything of himself and has no need to believe something without a formal proof, as he has already received a formal proof of every true thing, which can only happen as that man has sufficient faith in true things to experiment and learn of their truth with help from God. He has no faith because he no more has a mere hope in things not seen; he now sees all things.