SO WHAT IS THE CAUSE?
The cause of the person's distress may be useful to know in itself. That's because it could come out in the first conversation with them. It may be something like unforgiveness, disobedience or unrepented sin. (Check out Kingdom Forgiveness on the Menu.)
If a specific cause is known the Believer can confess it to the Father, repent, ask for forgiveness and thank Him.
Going through a process of trying to find a cause can be used by the enemy. If a cause is unknown, leave it that way! It makes no difference. Knowing what the "symptoms" are is enough.
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These "symptoms" are usually brought about when a Believer accepts a Satanic lie. That amounts to allowing him to torment.
However, the point is: the enemy has no authority or power over anyone who has truly repented and received Christ.
But authority may be ignorantly handed to him when a Believer has become vulnerable by being tricked into one of his "devices", or giving way to temptation.
Or perhaps Satan took advantage due to a Believer's ignorance of the word of Christ.
All in all, he is only able to exercise power over a Believer because of an opportunity to enter in the first place.
The enemy's primary and most frequently used device to gain entry is to challenge the word of Christ. He did it first with Eve (Genesis 3'1).
And He still poses the same innocent-sounding question: "Has God indeed said?". The result of what happened next is being felt right up to this moment.
Keep the word of Christ in mind:
"... lest Satan should take advantage of us;
for we are not ignorant of his devices,"
2 Corinthians 2'11.