Full Idea
It is the pinnacle of man's mendacity to think up a being as a beginning and 'in-itself', according to the yardstick of what he happens to find good, wise, powerful, valuable - and think away the whole causality by which they exist and have value.
Clarification
'Mendacity' is dishonesty
Gist of Idea
It is dishonest to invent a being containing our greatest values, thus ignoring why they exist and are valuable
Source
Friedrich Nietzsche (Writings from Late Notebooks [1887], 11[122])
Book Reference
Nietzsche,Friedrich: 'Writings from the Late Notebooks', ed/tr. Bittner,Rüdiger [CUP 2003], p.224
A Reaction
I think most non-religious people feel that religion completely fails to solve the problems it is meant to address, by just ignoring the problems, or pushing them to another place.