Eloisa to Abelard - Alexander Pope

I get the fundamentals of this poem, how Eloisa would rather keep her blissful memories of love than be like those in the convent who have experienced little, and subsequently have little to forget. The part that is of interest to me is the following:

Fill my fond heart with God alone, for he
Alone can rival, can succeed to thee.
How happy is the blameless vestal's lot!
The world forgetting, by the world forgot.
Eternal sunshine of the spotless mind!
Each pray'r accepted, and each wish resign'd;
Labour and rest, that equal periods keep;
"Obedient slumbers that can wake and weep;"


The line, 'eternal sunshine of the spotless mind', I've read, can be interpreted as ironic. My question is: how so? Thanks!

Brillisant simply brilliant!