Before his conversion, he was at least tolerant towards Christianity as per the edict of Galerius. His defeat of the pretender to the throne, Maximin (in 312), was supposedly precipitated by his an omen -- a flaming cross in the sky with the words, in Latin, "In this sign thou shalt conquer" (according to Eusebius). This began his long, slow slide into Christianity, and the Republic's eventual adoption of this religion as "official".
It is my opinion that there was no such revelation or dream before the Battle of Mulvian Bridge, and that the long, slow slide into Christianity was part of a political strategy designed to not only break with the pagans in Rome, but provide for a base in the eastern territories, i.e., Judea, to better defend against and attack the Middle and Near Eastern powers, like Persia. Aligning with the Jews/Christians in Judea would mean fewer internal military problems in the area and that soldiers would have been able to be recruited from them.
Also, there are many places in the Bible where subjects are taught to be deferential to their government, whatever form of government that may be. The populace is told to render under Caesar what is Caesar's -- i.e., taxes, if they should be under that dominion. They are told to turn the other cheek when hit, so they can be abused if necessary with little or no consequences. Look at the Bible from an administrative point of view, and it becomes a guidebook for how to rule over Christians.
This strategy appears to have worked until the Persian conquest of Jerusalem in 614:
