During the first century CE, Sethianism was a non-Christian baptismal sect. The Sethians considered themselves protectors of the primordial wisdom of Adam and Eve. These Gnostics also expected a visitation of Seth, messianic in nature. This first stage proudly bears the creation of the Sethian Sophia Myth, and the introduction of the Apocryphon of John.
Sethianism endures gradual Christianization in the first through second century, CE. Presumably, this occurred due to frequent contact with Christian groups in surrounding areas. During this time, the Sethians began to regard Seth and his father Adam as their pre-existent Christ. Seth and Adam transformed from human to supernatural beings. This time also provided finished products of the Apocryphon of Adam, the Apocryphon of John, the Hypostases of the Archons, the Thought of Norea and the Trimorphic Protennoia.
The later part of the second century proved to show Sethianismís estrangement from Christianity. Sethian doctrines became more orthodox and codified. Additionally, The Gospel of the Egyptians and Melchezidec are completed.
Ultimately, the third century marks the complete rejection of Sethianism by the Catholic church. Known for their individualistic mystical practices of Platonism, the Sethian Gnostics began to associate less with Christianity, and more with the Platonist tradition. Scholars believe this time embodied the Sethian adoption of Platonic metaphysical and numerological ideas. Allogenes, Zostrianos and the Three Steles of Seth are completed.
Finally, the late third century marks the end of Sethianism. Platonism changes names to Neoplatonism, and rejects the Sethian views entirely. Becoming increasingly fragmented, the Sethian Gnostics broke into several sub-groups. However, some continued writing. Before their final days, the Bruce Codex is completed. This important and elaborate text reflects a very sophisticated account of the various planes of existence, according to the Sethian tradition.
It is important to note that during the final two stages described above, Sethianism began reflecting monist views. Furthermore, the same stages also began to shed a positive outlook on the world and humanity.