We do not see into men’s hearts. We cannot judge, and are indeed forbidden to judge.
 C. S. Lewis, Mere Christianity (1952). copy citation

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Author C. S. Lewis
Source Mere Christianity
Topic heart forbidding
Date 1952
Language English
Reference
Note Adapted from a series of BBC radio talks made between 1942 and 1944
Weblink https://www.dacc.edu/assets/pdfs/PCM/merechristianitylewis.pdf

Context

“Now if once we allow people to start spiritualising and refining, or as they might say ‘deepening’, the sense of the word Christian, it too will speedily become a useless word. In the first place, Christians themselves will never be able to apply it to anyone. It is not for us to say who, in the deepest sense, is or is not close to the spirit of Christ. We do not see into men’s hearts. We cannot judge, and are indeed forbidden to judge. It would be wicked arrogance for us to say that any man is, or is not, a Christian in this refined sense. And obviously a word which we can never apply is not going to be a very useful word. As for the unbelievers, they will no doubt cheerfully use the word in the refined sense.” source