Take a look at the wiki link.
I think of that quote often as well but now I’m seeing it differently than before.
I interpreted it as advice to merely let resentment go but it could just as easily instead be to orient those feelings of resentment towards actually resolving what led to them in the first place.
Not just reflection but practice besides.
What would happen if God uttered to us a word?
I think they’re just hard to find?