Faith does not = believe. I can believe in something, then I can stop believing in something, we do it all the time, mulitple times throughout our lives, and even at times, during the day.
Believe is influenced by circumstances. That is why it is so wishy washy, because it is not rooted in trust, it is just rooted in an idea, It is rooted in self. Not in the thing which we are asked to trust. We have somethign we have already trusted in, and are asked to trust in somethign else. We may believe that thing to be true, and may try it out for awhile. But if we never ocme to trust that thing, it will never take root. We will always revert back to what we really trusted to begin with (an example is a jew, who tried the christian idea, but went back to law. Because law is where their real faith lay,)
Faith, on the other hand, is rooted in trust, in assurace (the greek makes this clear) which is far deeper than mere believe (rooted in an idea or what we think) and is not wishy washy, it depeneds not on the one who has the faith, but on the one who we are trusting in, As long as the one who we have faith continues to prove to be trustworthy, we will continue to have faith, the only way we lose faith, is if the person stops being truystworthy and is shown to be a fraud. Thats why faith in Christ can never be lost. Because it is rooted in him, not in ourself. (Saying we can lose faith means God becomes untrustworthy)