We (humans) like to know in advance or have things in advance, have it already there, and having it confirmed "in writing" is a plus.
It's not easy to have that level of trust and faith, without PROOF, you know?
But without faith it's impossible to please God.
What's interesting is that we DO have it in writing. We just lack the trust and faith to act on it, it seems (whatever that means). There are times where I took leaps and crashed, because it sure wasn't a leap of faith. A leap of fear rather.
I always think of this scene in "Indiana Jones and the Last Crusade" when I think of acting on and in faith with no physical evidence, etc. I think it describes it perfectly.