Felicity means happiness, a sense of peace and fulfillment.
Explanation:
Felicity is an English name, which comes from the Latin Felix, of felix, felicis. It means "happiness", "happy, blissful, lucky". In the excerpt, when the character began to feel "felicity" he was feeling, happiness, luck, comfort and joy.
I don't know a lot but I just did a class about this. But to change perfect past tense completed in the past by changing the verb is or could be by replacing the verb with the action to was ,did ,before, ect. I think this might help