Why did Constantine give Christians freedom?

Answer 1

Christians had already enjoyed relative freedom throughout the Roman Empire before the time of Constantine, as evidenced by the number of Christian churches that had been built, in addition to the traditional house-churches. However, Constantine lifted the persecution imposed by his predecessor, Diocletian. In fact, Constantine went much further, granting the mainstream Christian Church state patronage and commencing the persecution and plundering of pagan temples.

Constantine may have genuinely become a Christian: Gibbon believes not, saying that he was merely using the faith cynically for his own ends; others such as Michael Grant say that, although substantially motivated by the belief that Christianity would help achieve his imperial aims, Constantine was more motivated by genuine Christian belief. Certainly Constantine believed that a dominant, united Christian Church would help maintain a united Roman Empire. It was one of his greatest disappointments that he was unable to achieve Church unity.