The Great Prophets knew that uncovering the secrets behind the True God's messenger was too arduous, even more so than storming the Temple of Knowledge and facing the Servants of Knowledge head-on, with a much lower success rate.
That's why they chose this last path.
For if the secrets behind the True God's messenger could have been easily deciphered, the Servants of Knowledge would have already discovered the method to Save the World, and there would have been no reason for their betrayal of the True God.
According to the deductions made from the Abyss Oracle, the Servants of Knowledge turned to the enemy because they had no other choice and were willing to merge with them after the resurrection of the Abyss Massed Stars.
The Prophets did it for the world's brief continuation, and the Servants of Knowledge did it to retain the 'Omniscient Authority' after the destruction and re-creation of the world...
