The document provides commentary on Isaiah 21, which prophesies the destruction of Babylon by the Medes and Persians. It discusses various interpretations of the phrases "desert of the sea" and "whirlwinds in the south." The commentators generally agree that "desert of the sea" refers to the marshy plains around Babylon, which were like a sea before being drained, and that "whirlwinds in the south" describes the invading army's rapid advance from the deserts of southern Media and Persia like powerful storms. The commentary also notes historical accounts stating the area was originally marshland and outlines the key events of Cyrus' conquest that fulfilled this prophecy.