Schaff, Philip. History of the Christian Church (The Complete Eight Volumes in One). Amazon Kindle Edition, 2014.
Volume 2, Ante-Nicene Christianity A.D. 100-325, “Chapter 5. Christian Worship” (Includes an introduction and sections 59-74).
§61. The Christian Passover. (Easter).
Schaff observes that in the Ante-Nicene period the church would celebrate Easter, Pentecost, and Epiphany (Schaff 2014, Loc. 14867). In general, the celebration of the Lord’s Day was seen as a day of resurrection, akin to Easter. Because of its close ties to the suffering of Christ, the recognition of a form of Passover, centered around the death of Christ, emerged at Good Friday (Schaff 2014, Loc. 14892). Over time, the period of mourning before Good Friday extended to the current boundaries of Lent. Likewise, after the time of Easter, it was natural to recognize a season of Pentecost, the time of activity in the church.