“A prayer

Of Habakkuk,

The prophet,

According to Shigionoth.”

This last chapter is clearly a prayer or hymn of Habakkuk the prophet.  Like the psalms attributed to David, it may not have been written by him, but inspired by Habakkuk.  They were to sing this using the melody of Shigionoth or a lamentation.  Thus, this hymn or prayer may have been used in their worship services.