Fact because a fact is tested and proven already
Hope it helps yah (. ❛ ᴗ ❛.)
I believe that the idea which is addressed in the passage above is friendship and love.
You can see that there is a strong friendship between Lancelot and Arthur, even though Lancelot is seeing his wife behind his back. On the other hand, we can see the theme of love between Lancelot and Guinevere, even though Arthur is not aware of that.
It means the way the writer uses the language to convey meanings, feelings e.t.c. In another context it may mean the way the writer uses language in order to manipulate the reader and lead him where he/she desires e.g. to feel in a certain way about a character, to have certain expectations e.t.c.