The thoughts of your heart revealed
When Simeon is in the temple and Jesus is presented to Him, he prophesies to them that this child will cause the rising and falling of many in Israel, to be a a sign that will be spoken against so that the thoughts of many hearts will be revealed. Such was the impact of what Jesus would do that it would provoke a reaction that people would verbalise. The response in their hearts would not be able to be contained, what they felt would overflow – self condemning.
We see it today, the ministry of Jesus causes deep reactions in people. They are either for Him or against Him. Which ever direction they are facing there seems to be an involuntary reaction to speaking out that which is in their hearts.