By the second century, perhaps much earlier, Christianity was divided into two main branches - what is now known as the proto-Catholic-Orthodox branch and Gnosticism. While the proto-Catholic-Orthodox branch was disciplined and and developed a hierarchical structure, Gnosticism generally felt no need to enforce discipline among its members nor to have bishops as overseers. Gnostics were encouraged to seek direct access to God by prayer and revelation, rather than through the clergy.
Athanasius, bishop of Alexandria, sought to block anyone seeking direct access to God. In On the Incarnation of the Word, he explained that human sin had damaged that image beyond human repair. Augustine later developed this into his understanding of "original sin". Augustine himself was a Manichaean before joining the Catholic Church.
While there was a good deal of antagonism between the two branches, there was also an interchange of religious ideas. The Gnostics were prolific authors and wrote numerous gospels and other books. The Gospel of Thomas and possibly the Gospel of John were written in the Gnostic milieu and later adopted by orthodox Christianity, with modifications to remove much of the gnostic content. The Gospel of Thomas had strong support for inclusion in the orthodox New Testament.
Gnostic Christians often attended orthodox church servoices, not only as places of worship, but also in order to recruit members to Gnosticism.
Gnosticism was a belief system that emerged in the early Christian era, challenging traditional Christian teachings. It influenced the development of Christian doctrine by promoting alternative ideas about the nature of God, the universe, and salvation. The early church responded by clarifying and solidifying its core beliefs, leading to the formation of orthodox Christian doctrine.
No book in the bible addresses Gnosticism, you are looking for Against Heresies as written by a father of the church, Irenaeus.
GNOSTICISM
The opponents of Gnosticism were primarily early Christian leaders and theologians, such as Irenaeus and Tertullian. They argued against Gnosticism's belief in secret knowledge and its rejection of the material world, emphasizing instead the importance of orthodox Christian doctrine and the belief in a loving creator God.
Gnosticism was considered dangerous by early Christian leaders because it challenged orthodox beliefs and undermined the authority of the established Church. Its emphasis on secret knowledge and personal spiritual experience threatened the communal and doctrinal unity that early Christianity sought to maintain. Additionally, Gnosticism often rejected the material world as evil, which contradicted the Christian teaching of creation and the incarnation of Christ, potentially leading followers away from mainstream faith practices. This perceived threat to theological stability and social order prompted efforts to suppress Gnostic teachings.
Irenaeus was an early Christian theologian who lived in the 2nd century. He is known for his defense of orthodox Christianity against various heresies, particularly Gnosticism. Irenaeus emphasized the importance of apostolic tradition and the unity of the Church in combating false teachings.
Gnosticism is generally believed to have emerged in the early centuries of the Common Era, around the 1st to 2nd century AD, although its roots may trace back to earlier philosophical and religious traditions. It is characterized by its diverse beliefs and emphasis on personal spiritual knowledge (gnosis) over orthodox teachings. Gnosticism flourished alongside early Christianity but was eventually deemed heretical by mainstream Christian authorities.
Gnosticism is significant in the Bible because it was a belief system that influenced early Christian thought. Gnostics believed in secret knowledge for salvation and had different views on the nature of God and the material world. This led to debates and conflicts within early Christianity, shaping the development of Christian theology.
Gnosticism can be read about in many books. The Gnostic Society has their own Library in which everything about the Gnosticism can be learned or studied.
The origin of Gnosticism is generally believed to come from 3 main sources: Much of its philosophical tendencies came from Platonism, speculations on the origin of evil may have come from the Persian religion and the Buddhism of India may have been the origin of the doctrine of antagonism between matter and spirit. Gnosticism was named for "gnosis = knowledge" and was mainly concerned with the origin of sin rather than how one is saved from sin.
Gnosticism does not have a single founder as it emerged from diverse religious and philosophical influences in the ancient world. However, it is believed to have been shaped by various early Christian and Jewish sects, as well as elements of Hellenistic and Persian mysticism.
there is no scientific basis for Gnosticism or orthodox (mainstream) Christianity.