Gnosis is contained within many religions and paths. Technically it is called the path of the spirit or soul path. Many religions teach everyone has a soul (nafs in islamic gnosis). The religions teach our soul is impure and unworthy so we have to watch what we do, not to go against gods law or think bad thoughts.
Through purification we can reach unity with god, through Fanna. This is a dualistic approach which is easily accessible to anyone.
Non dual gnosis is different as it reveals the ultimate outlook, the essence of god (zat). Through knowing the essence and becoming familiar with it, results in recognition of the divine. Put simply the utilimate view is – God is one and if god is one there cannot be another.
All the prophets preached God is one, this is the esoteric meaning. In Arabia, god is the creator and creation, This is because god essence (zat) is the essence of all things.