This reading is Daniel 10.
The messenger isn’t identified by name, but he appears to be Gabriel, the angel who has already appeared to Daniel. Some think it may be Christ, but that would mean Daniel’s vision was of Christ and that a messenger came as well. For Christ would not have been hindered for 21 days as the messenger was (v. 13).
This passage shows how real, serious and active spiritual warfare is. It reminds me of Ephesians 6:10-12:
Finally, be strong in the Lord and in his mighty power. Put on the full armor of God so that you can take your stand against the devil’s schemes. For our struggle is not against flesh and blood, but against the rulers, against the authorities, against the powers of this dark world and against the spiritual forces of evil in the heavenly realms.
Daniel was obviously exhausted, anguished and fearful. The angel calms his fears and sets up the prophecies to be given in chapters 11 & 12.
The next reading is Daniel 11.