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).
§71. The Doctrine of Baptism.
The earliest Christians considered baptism as the means of entry into the Christian faith. In the case of adults it would follow instruction (Schaff 2014, Loc. 15436). Schaff summarizes Justin and Tertullian describing baptism as a washing which regenerates, cleansing from sin. Belying his own view of baptism, Schaff says of Tertullian, “He already leans towards the notion of a magical operation of the baptismal water” (Schaff 2014, Loc. 15444). Yet repentance and faith were required.
Schaff notes Clement of Alexandria and Hermas taking a position that the Old Testament saints were somehow baptized in Hades. Many agreed that, in case of martyrdom, baptism would be considered accomplished (Schaff 2014, Loc. 15444). However, baptism was widely understood to forgive only sins committed before baptism. This led to delaying baptism until the death bed. For sins after baptism, Tertullian and Cyprian agreed there should be acts of penance, which became a sacrament. “Tertullian held seven gross sins, which he denoted mortal sins, to be unpardonable after baptism, and to be left to the uncovenanted mercies of God…” (Schaff 2014, Loc. 15457).
Schaff states that baptism, even in Constantine’s time, was primarily applied to repentant adults. Application to children was problematic because an infant cannot receive instruction and renounce the devil (Schaff 2014, Loc. 15459). tertullian saw baptism as a consecratory act to be followed by instruction and conversion. To supplement the rite, confirmation was later added (Schaff 2014, Loc. 15466).