“If only one could come back to this quiet place, where only intellectual achievement counted […] then, one might be able to forget the wreck and chaos of the past, or see it, at any rate, in a truer proportion.” 

Harriet is expressing why she’s so drawn to Oxford as a haven from the world. This is especially true given her own scandalous past. She sees the place as a refuge from her past bad choices and a defense against future mistakes.

“Here was a fighter, indeed; but one to whom the quadrangle of Shrewsbury was a native and proper arena: a soldier knowing no personal loyalties, whose sole allegiance was to the fact.” 

Harriet is describing her first impression of Miss de Vine. She admires the scholar’s unswerving devotion to truth. Ironically, it is this very dedication to cold, hard fact that triggers the string of disasters that follow in the novel. 

“The fact is, thought Harriet, I have got a bad inferiority complex; unfortunately, the fact that I know it doesn’t help me to get rid of it. I could have liked him so much if I could have met him on an equal footing.” 

Harriet is revealing one of the reasons why she’s rejected Wimsey’s proposals. Personal indebtedness to the man who saved her life isn’t a good reason to marry someone. As an independent woman, Harriet can’t tolerate the subordinate position in which she finds herself relative to Wimsey.