Swami Mukundananda
Why must I give up resentment if I want to do bhakti?
Resentment steals the mind from bhakti
When the mind keeps thinking that a person is very bad, it is remembering that person instead of God and Guru. Both attachment and hatred need to be released to free the mind to do bhakti, devotion to God.
So, "This person is very bad, this person is very bad." Now instead of remembering God and Guru you are remembering that person, just as you would remember an attachment, in the same way you are remembering in hatred.