I picked up Einstein and Religion the other day. Its been a compelling read as I am about 1/3 through in just over 24 hours. Both of these come from pages 74-75.
Maimonides:
Our Knowledge [of God] consist in knowing that we are unable to comprehend Him.
Spinoza:
On your question whether I have a clear idea of God as I have of triangle, I would answer in the affirmative; but on your question whether I have a clear image of God as I have of triangle, I would answer in the negative. For of God no image can be made.
