"As with Hippolytus’s other imagined “Gnostic sects,” it’s virtually certain that no sect called the “Sethians” ever existed in antiquity."
https://gnosticismexplained.org/the-classic-gnostics-sethians/
"The Sethians, one of many ancient Gnostic groups, flourished in the Mediterranean region at the time of nascent Christianity. It is probably older than the first Christian churches. Predominantly Judaic in foundation, and strongly influenced by Platonism, Sethianism provided a synthesis of Judaic and Greek thought with its own distinct interpretation of cosmic creation. The group derived its name from veneration of the biblical Seth, third son of Adam and Eve. Sethian creation myths portray him as a divine Incarnation."
https://www.newworldencyclopedia.org/entry/Sethianism
"They were the true founders of what we know as ancient Gnosticism one of many Gnostic groups that had flourished in the North Africa and around the Mediterranean region, and especially in ancient Egypt, the island of Crete, Cyprus, mainland Greece and Rome at the time before and during the formations of early Christianity."
https://gnosticwarrior.com/sethians.html
"Sethian Gnosticism, also called Classical Gnosticism and Sethianism, is named after Adam’s third son Seth and the divine Seth, and had its ‘golden age’ from about 300BC to 300AD.
The Sethian tradition is probably the oldest of the Gnostic schools with common sacraments, a basic systematical theology, and a core Mystery in which the Sethians were inducted.
During the first period of about 600 years, our Gnostic tradition had three major reforms as reflected in the texts that were found buried at Nag Hammadi in Egypt.
This collection of texts, the most important discovery of Gnostic literature, was probably buried since these writings were forbidden by canonical Christianity"
https://www.charaxio.org/sethianism.html
"Sethians, then, were a very important Gnostic sect. They believed themselves to be direct descendants of Adam and Eve through Seth. Since Seth was the keeper of secret knowledge, his followers (Sethian Gnostics) were the only ones who had the true knowledge"
https://biblewise.com/bible_study/questions/sethian-gnostics.php
"Sethian refers to a main Gnostic cult of the 2nd-3rd centuries AD. They claim to possess gnosis/knowledge preserved from Adam and Eve’s son Seth and from Noah’s wife whom they named Norea. Sethians are mentioned in the 2nd century AD works of Irenaeus and Pseudo-Tertullian."
https://truefreethinker.com/serpent-seed-of-satan-in-sethians-kabbalah-islam-and-moonies/
"Sethianism was a Gnostic sect during the Roman era. The Sethians heresy, at the same time as Valentinianism, was one of the main Gnostic belief during the 2nd to 3rd centuries. Their belief, strongly Judaic in nature, was arguably influenced by Platonism. Sethianism attributed its origin to Seth, the third son of Adam and Eve and Norea, the wife of Noah (who also plays a role in Mandeanism and Manicheanism).
This heresy was condemned by Irenaeus, Hippolytus, and Philaster.
The Sethian sect was founded around the Apocalypse of Adam, discovered in 1946 as part of the Nag Hammadi library (codex V.5)."
https://www.catholicdoors.com/faq/qu954.htm
"These systems believed that the material world is created by an emanation or ‘works’ of a lower god (Demiurge), trapping the divine spark within the human body. This divine spark could be liberated by gnosis, spiritual knowledge acquired through direct experience. Some of the core teachings include the following:
There is an unknowable God, who gave rise to many lesser spirit beings called Aeons.
The creator of the (material) universe is not the supreme god, but an inferior spirit (the Demiurge)."
"Historical evidence suggests that Sethians were regarded as heretics by church leaders, and by the time this book was written, they had mostly been wiped out."
https://www.iflscience.com/environment/researchers-decipher-ancient-egyptian-spellbook/