The Foolishness of the evil one
The devil is real and his temptations are real. He hates you with a pure hate and desires your destruction. This is good to know. But the evil one is also quite shrewd and manipulative and will rarely speak blatant lies to you since he knows this temptation will most likely not convince you. Instead, he seeks to speak confusion to you, identifying things that are partly true and mixing them with subtle lies so as to lead you astray. You may find that you begin to obsess about this thing or that. And you may find that your reasoning might make some sense, but you begin to experience a sadness and confusion as you think. Stop thinking in those moments and run to the Mercy of God. When your thinking is immersed in God, you are left refreshed and light. You begin to have new joy and clarity. But when the evil one begins to have his way with you, the opposite effects are felt in your soul. Be attentive to his sneaky deceptions and pay no attention to them (See Diary 1497-1499).
Devotion to the souls in Purgatory contains in itself all the works of mercy, which supernaturalized by a spirit of faith, should merit us Heaven. de Sales