In Annabelle: Creation, towards the end before Sister Charlotte was killed, she chanted something.
What verse is that?
Why did it have no effect on the Devil?
I am not sure on the verse part, but as you must have seen in few old horror movies/conjuring/conjuring 2, a person must have a strong faith in God along with the courage to say out the verse correctly. Sister Charlotte was not experienced in dealing with the Devil/Evil entity (similar to the church priest, who was attacked in Annabelle, outside the church), so she was attacked and killed easily.
You may also refer to the movie 'fright night' (90's movie), where this theory was explained by a vampire itself.