If, as Our Lord tells us, “Thus you will know them by their fruits.” (Matthew 7:20) then I don’t see how the Marian apparitions at Fatima, (or any that the church has approved) can be said to have been from the devil, since the message is one of repentance, holy living, and faith in and devotion to Christ.
Would the devil bring a message that works against his own aims?
Our Lord spoke of this in the 3rd chapter of the Gospel of Mark.
23: And he called them to him, and said to them in parables, "How can Satan cast out Satan?
24: If a kingdom is divided against itself, that kingdom cannot stand.
25: And if a house is divided against itself, that house will not be able to stand.
26: And if Satan has risen up against himself and is divided, he cannot stand, but is coming to an end.
27: But no one can enter a strong man’s house and plunder his goods, unless he first binds the strong man; then indeed he may plunder his house.
28: “Truly, I say to you, all sins will be forgiven the sons of men, and whatever blasphemies they utter;
29: but whoever blasphemes against the Holy Spirit never has forgiveness, but is guilty of an eternal sin” –
The Lord also dealt with this in Luke 11.
16: while others, to test him, sought from him a sign from heaven.
17: But he, knowing their thoughts, said to them, "Every kingdom divided against itself is laid waste, and a divided household falls.
18: And if Satan also is divided against himself, how will his kingdom stand? For you say that I cast out demons by Be-el’zebul.
19: And if I cast out demons by Be-el’zebul, by whom do your sons cast them out? Therefore they shall be your judges.
20: But if it is by the finger of God that I cast out demons, then the kingdom of God has come upon you.
From the context of these passages and the clear fruits of righteousness and loving devotion the Our Lord that have resulted from this and the other approved appparitions I would have to conclude three things.
*]Mary’s message has never changed. “Do whatever he tells you” (John 2:5)
*]The fruits are good therefore the tree is also good.
*]It may be unwise for those skeptics to make an allegation that these are of the devil.
Pax Domini sit semper vobiscum.