Diary of St. Faustina...on how satan hates the Divine Mercy

1405   -  November 30, 1937. When I was going upstairs this evening, a strange dislike for everything having to do with God suddenly came over me. At that, I heard Satan who said to me, "Think no more about this work. God is not as merciful as you say He is. Do not pray for sinners, because they will be damned all the same, and by this work of mercy you expose your own self to damnation. Talk no more about this mercy of God with your confessor and especially not with Father Sopocko and Father Andrasz.” 

At this point, the voice took the appearance of my Guardian Angel, and at that moment I replied, "I know who you are: the father of lies [cf. Jn. 8:44]." I made the sign of the cross, and the angel vanished with great racket and fury.