Gnosis is a foreign word that means “knowledge.” The “Gn” part of the word is pronounced like “gnat.”
Gnosticism is a loosely connected set of ideas held by groups of people who believe that there is “hidden knowledge” that is only accessible to the “enlightened” or “invited.” Kabballah, Freemasonry, Shriners, Buddhists, Hindus, alchemy, and a hundred forms of witchcraft argue about the proper definition of Gnosticism. Some of the various bits of “knowledge” that the various groups (and Christian theologians and historians) argue about include dualism, which is the idea that matter is evil and spirit is good, that good and evil are false concepts that exist only in the minds of unenlightened people, that all religions lead to god, that a person can only be delivered from this evil, fallen world by receiving enlightenment from outside it.
What is the difference between these types of teachings and what Jesus answered when He was quizzed about why He taught in parables? His answer to that question was, in essence, “So they won’t understand.” To His disciples, He added, “The ability to understand has been given to you.” (Luke 8:10)
One of the tenants of Gnosticism is the idea that salvation comes by special knowledge. I can think of many “Christian” groups who lead their people to believe exactly that – if you don’t have their baptism, their rituals, their code words or handshake, you are not “going to heaven.”
So what is different about what Jesus was teaching, and the way He was teaching it? The “knowledge” with regard to salvation is “knowing” Him. It is not the acquisition of information – it is the surrender to a relationship.
The “knowledge” with regard to the Kingdom is “knowing” what He is instructing you to do with your life. Clues are found in books or teachings, but the real answers are only found by listening to the Spirit of the King, and the real advance in that knowledge is found in obedience.
The two judgements all humans will face are related to getting these two bits of “knowledge” correct: having my name written in the Lamb’s Book of Life, and entering the Kingdom of Heaven by obeying the King of it (Revelation 20).