It means cunning as well as broad comprehension.

And the modern Englishman, in all times and in all countries, trusts especially to this faculty, which is very largely developed in the race to which he belongs.

No Englishman believes in working from book learning.

He suspects all theories, philosophical or other.

He suspects everything new, and dislikes it, unless he can be compelled by the force of circumstances to see that this new thing has advantages over the old.