Cherish your doubts, for doubt is the handmaiden of truth.
Doubt is the key to the door of knowledge.
It is the servant of discovery.
A belief which may not be questioned binds us  to error,
for there is incompleteness and imperfection in every belief.
Doubt is the touchstone of truth.
It is an acid which eats away the false.
Let none fear for the truth, that doubt may consume it; for doubt is a testing of belief. 
For truth, if it be truth, arises from each testing stronger, more secure.

Those who would silence doubt are filled with fear.
The house of their spirit is built on shifting sands.
But they that fear  not doubt, and know its use, are founded on a rock.
They shall walk in the light of growing knowledge.
The work of their hands shall endure.
Therefore, let us not fear doubt, but let us rejoice in its help;
it is to the wise as a staff to the blind.
Doubt is the handmaiden of truth.
--from Gates of Prayer (Siddur)