"I do not know just what they were, never having heard him explain them in detail; but I am very sure he gave no outward indication of his mind having undergone any change while here."
If you don't know nor cannot estimate someone's thoughts at all, how do you know you can safely exclude any change???
And if you read correctly, Nicolay just said "he gave no outward indication". Translation IMO - "I didn't see/hear/know anything at any time. I cannot comment on what was nor what might have happened." "I am very sure" in the context of the sentence could as well mean "I assume (but what do I know...)".
To me this is just a most diplomatic statement that leaves every possibly open and involves the speaker the least. I think Nicolay simply didn't want to comment in any way on such touchy subject that easily could evoke "gossip" and further speculations of all kind.
Lincoln and religion
