Fr. Troy Pierce writes at the Path of Gnosis:
One of the common misunderstandings when you tell people that you are a Gnostic is that they hear the more familiar word “Agnostic.” (This becomes quite amusing when they mishear “Agnostic Priest,” or “Agnostic Eucharist.”) This becomes a good opportunity to elucidate one of the truisms of contemporary Gnosticism: You have to be an Agnostic before you can become a Gnostic.
The original differences between agnostic and gnostic are the “privative alpha” of Classical Greek. This prefix functioned like “un-” or “non-” and thus linguistically the two words are opposites, literally ‘Knower’ and ‘Un-Knower.’ (incidentally, the “a” was the first syllable, and the “g” was pronounced in both.)
However, this is Modern English and not Classical Greek, and so both terms have come to have certain more specific meanings. An Agnostic has been jokingly called a “cowardly Atheist,” but is generally someone who knows that they do not know about the divine from the reports of others.
As William James says, most people have faith in someone else’s faith. They believe they know because they have beliefs that have been given to them. While this is entirely satisfactory in some aspects of life, for example if someone tells you what they know about Aruba from their readings, it is unlikely that you will have a need or desire to check their facts, you are satisfied with their account. However, It is highly unsatisfactory when it comes to the truly important aspects of life: the ultimate nature of oneself, the Cosmos, and the Divine.
In rejecting the answers of the Believers, the Agnostic withholds belief, and knows that he does not know. Someone who mistakes belief for knowledge, as most do in this world, will wrestle with the question of existence in the manner of belief: seeking stronger belief and assuaging doubts. It does not occur to Believers that they do not know, it only occurs to them that they do not believe. Thus an Agnostic has made a great deal of progress towards becoming a Gnostic, and has developed the attitude a Gnostic must have. For while a Gnostic knows from experience (has gnosis of), there is so much that a Gnostic does not know (has no gnosis of), and in these matters must maintain the attitude of an Agnostic. We can turn to scripture, tradition, and others for guidance in those aspects for which we personally have no Gnosis, but we cannot have Gnosis of someone else’s Gnosis.
To know that one does not know is the starting point of the path of Gnosis.