Eternal sunshine of the spotless mind! Each pray'r accepted, and each wish resign'd?”
Appreciating these lines calls for some background understanding. So here is some history you might wanna dig into—
The poem is based on the clandestine love and subsequent marriage of Héloïse d'Argenteuil to Peter Abélard, her teacher. Abélard insisted that she keep their marriage a secret as it might mar his reputation. However, as the word spread, Abélard persuaded Héloïse to take the vow of silence in the convent of Argenteuil, for her own safety. This act of his was perceived by her family as his attempt to get rid of her. They sought their vengeance by castrating him. Completely mortified, Abélard became a monk in the Abbey of St Denis in Paris. After several years of agonizing separation,
Héloïse's feelings for Abélard were revived. So they exchanged four letters, where they expressed their indignation, anguish and consternation. However, their conflict of opinions left them both feeling bitter. So she decided on living in solitude than spend an eternity with him.
Now, back to the point –
1--- How happy is the blameless vestal's lot!
2--- The world forgetting, by the world forgot.
3--- Eternal sunshine of the spotless mind!
4--- Each pray'r accepted, and each wish resign'd ..
1--- The nuns (chaste women) who devote their life to serving God are cut off from the world and happy due to their ignorance.
2---The vestals forget the world and the world reciprocates it for them. Neither of them has the need to think of the other.
3--- A mind that does not dwell upon the tribulations of the past and dissociates itself from any ingrained feelings experiences true bliss, comparable to an “eternal sunshine”.
4--- Héloïse feels happy about the fact that her prayer for lapse of memory on events that had bothered her over the years had been answered. Also, she voluntarily demits herself from her wish to be reunited with her long-lost love when she comes to terms with the fact that he never truly loved her. (Reference - Héloïse d'Argenteuil)
These lines are quoted by Mary Svevo in the movie “Eternal Sunshine of The Spotless Mind”. She also quotes Nietzsche (“Blessed are the forgetful: for they get the better even of their blunders”) in the same scene, thus supporting the above idea.