A couple of things though:
“Unlike most contemporary Christian authors (conservative or liberal) Willard makes a rather interesting and unique claim: Christians must demonstrate a verifiable form of spiritual knowledge.”

I think this is important, unless claims of spiritual knowledge are verifiable those of us with a skeptical bent will reject them. That knowledge must be testable against the realities of life and the insights of others, otherwise it won’t be distinguishable from stuff that has been made up.

I also agree with you on this:
“Some of the atheists I’ve encountered are atheists, in my estimation, precisely because they do long for what God supposedly stands for – such as righteousness, peace, and justice – but they cannot reliably find that God in the world around them,”

I think this is a factor in may atheists beliefs.