The Greatest Saints

I read a quote recently that said something to the effect that we would be surprised if we really knew who are the greatest saints. I think it came from C.S. Lewis, but I don't recall. I brought this up in Bible class this morning when the discussion began to revolve around what makes someone "a strong Christian." I replied that I hate that term ... it can discourage and bring doubt to those who feel weak in faith ... not to mention the fact that it focuses on the individual's faith and not on Christ and the gifts He gives.

I "googled" a few words to find the quote, but am still looking for it. However, I did find this interesting passage from a book by Roman Catholic apologist Peter Kreeft:

"The greatest saints have always had the greatest joy - indeed, one of the things the Church looks for in canonizing saints is heroic joy in their lives, for joy is one of the fruits of the Holy Spirit (Gal. 5:22). Yet these same saints are also the most emphatic about their being sinners. The greatest saints see themselves as the greatest sinners. And the greatest saints are not the greatest fools ... Pascal said that there are only two kinds of people: saints, who know they are sinners, and sinners, who think they are saints. Socrates said something similar: that the wise are those who know they are fools and the fools are those who think they are wise." (from Catholic Christianity, page 337)

If any of you know what quote I'm referring to, I'd love to have your help with the exact quote and who said it or wrote it.