Final answer:
Gnosticism did not deny the existence of Jesus but viewed him as a source of secret knowledge for individual salvation, challenging orthodox Christianity's centralized authority and leading to its denouncement as heretical.
Step-by-step explanation:
Gnosticism was a religious movement that emerged in the early Christian era, presenting a significant challenge to orthodox Christian beliefs. Contrary to what your question suggests, Gnostics did not deny the existence of Jesus; rather, they perceived him as a secret revealer, someone who imparted esoteric wisdom that could lead to divine union. Gnostics believed in a complex cosmology involving a series of divine emanations and placed a heavy emphasis on personal spiritual knowledge ('gnosis') over the institutionalized church and its rituals. They indeed believed that Jesus communicated hidden knowledge that could empower an individual to achieve salvation and possibly wield influence on Earth when properly harnessed through rituals that the Gnostics considered to be like incantations comprising secret 'names of God'. Due to its secretive nature and divergence from emerging orthodox Christian doctrine, Gnosticism was branded as heretical by the early church, particularly after the definition of orthodoxy began to solidify in church councils, such as the Council of Chalcedon in 451. The Gnostic viewpoint competed with other interpretations of Christianity on many theological fronts, most notably the nature of Jesus Christ and the route to salvation.
It's important to note that the Gnostics' reluctance to proselytize their beliefs and their distinctive view on Jesus and salvation was vastly different from the developing orthodox Christian standards, which sought to formalize a set of beliefs and unify the Christian practice under those tenets. This aspect of Gnosticism, among others, was perceived as a threat to the unity and authority of the orthodox Christian church. Furthermore, the notion that salvation can be personally accessed through secret knowledge rather than through the church was another point of divergence that Orthodox Christianity found threatening and heretical.