Though believers have trusted Christ as their Savior, and have committed their lives to Him, they can become unwitting tools of Satan. The Bible provides some examples of this unfortunate occurrence.

1. David Numbering Israel

The Bible gives the account of David numbering Israel.

And Satan stood up against Israel, and moved David to number Israel (1Ch 21:1).

Satan was the motivating force behind David numbering the people. David's sin caused divine judgment against the nation.

Permission of the Lord

We find that the ultimate permission for David to number Israel came from the Lord.

And again the anger of the Lord was kindled against Israel, and He moved David against them, saying, Go, number Israel and Judah (2Sa 24:1).

Again, Satan could not incite David unless he was given divine permission. Yet David chose to be a tool of Satan in his numbering of Israel.

2. Peter And Jesus

We also have the account of Jesus rebuking Peter and calling him "Satan."

And Peter took Him, and began to rebuke Him, saying, Be it far from You, Lord: this shall never be unto You. But He turned, and said unto Peter, Get behind Me, Satan: you are a stumbling-block unto Me: for you mind not the things of God, but the things of men (Mat 16:22-23).

When Peter attempted to get Jesus to bypass the cross, he was speaking as an instrument of the Devil. Jesus addressed him in that manner.

Summary

Believers can unwittingly become tools of the Devil. We discover this with the case of David numbering Israel, as well as Peter rebuking Jesus for speaking of the cross. Therefore believers can come under satanic influence, and do things that are contrary to God's will and plan.