There are situations that require the sudden and immediate manifestation of God's power.
The power of God was brought to bear in Paul and Silas' situation in response to their praise and worship of God, and their expectations. They chose to praise and worship in the face of a seemingly impossible situation.
When God's presence fills you and your environment up nothing can contain it. The foundations of the issues will be shaken up suddenly. And immediately great doors will be opened and all of the things holding you down/chained will be loosed. All by the supernatural power that accompanies His presence.