The precise meaning of the surprising turn of events that in 311-313 gave freedom to Christianity is still a matter of debate. It seems, however, that the recent interpretation by the Dutch theologian Hendrik Berkhof has cleared up the mysterious affair as far as the sources allow.
The persistence and survival of the Christians under violent persecutions apparently convinced the regents Galerius, Licinius, and Constantinus that the Christian God was powerful enough to protect his followers in adversity; that he was a reality that should be treated with caution. The Edict of Galerius, of 311, explained that as a consequence of the persecutions the Christians neither fulfilled their cult obligations to the official gods nor worshiped their own God in proper form.
This observation apparently motivated the sudden change of policy. If the powerful God of the Christians were not worshiped by his own adherents, he might take his revenge and add to the troubles of the rulers who prevented his worship. It was the good, solid Roman do-ut-des principle. In return for their new freedom the edict ordered the Christians to pray for the emperor, the public weal, and their own. This was no conversion to Christianity but rather an inclusion of the Christian God into the imperial system of divinity.
The Edict of Licinius, of 313, stated that the former anti-Christian policy had been revised "so that all that is of divinitas in the celestial habitat be propitious to us and all who are under our rule."
The curious term divinitas was reconcilable with official polytheism and the recognition of the Summus Deus of the empire religion, and at the same time it sounded monotheistic enough to make Christians happy. The suspense of meaning was probably intended—one feels in it the deft hand of the Constantine, who later, in the christological debate, insisted on the sublimely meaningless homo-ousios.