The fourth century is important in Christian history because it is considered by many Church historians as the period in which the Church finally came of age. It was a period, in the wake of the Edict of Toleration, in which Christians emerged from centuries of persecution, intellectual ridicule and social marginalisation to be the dominant group within the social and religious life of the Roman Empire. The exact opposite was to happen to the Jews, “at the close of the previous century, [the Jews] were no more than a special type of unbeliever; at the end of the fourth, a semi-satanic figure, cursed by God, and marked off by the State”.
This is a short 1500 word but enlightening essay on this critical period with a good bibliography. You can find the PDF here.