Denethor’s Unwelcoming Manner

[Lotessa]

I’ve been puzzling about Denethor’s caution towards Gandalf when he requested to see Denethor’s scrolls and books:

Less welcome did the Lord Denethor show me than of old and grudgingly permitted me to search among his hoarded scrolls and books.

This is from The Council of Elrond when Gandalf was giving an account of what he had been doing over the years.
I have been wondering why Denethor was reluctant to let Gandalf look at his scrolls.

Thanks.

~Lotessa