This song is a versification of Isaiah 40:1-5, the passage that opens the final large group of prophecies in Isaiah 40-66. Many of these prophecies express consolation and hope that Judah's exile in Babylon is almost over. That is certainly the tone of 40: 1-5-words of comfort forecasting a new reign but also words that call for proper preparation–that is, repentance.
This biblical text opens the second section of prophecies by Isaiah (ch 40-66), which is characterized by offers of consolation and further calls to repentance.
Bert Polman